Apparatus and Method for Treating Waste Water Containing Ammonium Salts

ABSTRACT

In a method for treating waste water containing ammonium salts, sodium sulfate crystal is obtained by freezing crystallization, then the pH value of the waste water is adjusted to a specific range, and next sodium chloride crystal and ammonia water is obtained by evaporation. Alternatively, the pH value of the waste water is adjusted to a specific range, then sodium chloride crystal and ammonia water is obtained by evaporation, and next sodium sulfate crystal is obtained by freezing crystallization. This method can recover ammonia, sodium sulfate, and sodium chloride from the waste water.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to Chinese Application Nos.201710752805.5 and 201710751942.7 entitled “Method for Treating WasteWater Containing Ammonium Salts” and Chinese Application Nos.201710752394.X and 201710750767.X, entitled “Method for TreatingCatalyst Production Waste Water”, which are specifically and entirelyincorporated by reference.

FIELD OF THE INVENTION

The present invention relates to the waste water treatment field,particularly to apparatus and method for treating waste water containingammonium salts, more particularly to apparatus and method for treatingwaste water containing ammonium salts, which contains NH₄ ⁺, SO₄ ²⁻, Cl⁻and Na⁺.

BACKGROUND OF THE INVENTION

In an oil refining catalyst production process, large quantities ofinorganic acids, alkalis and salts, such as sodium hydroxide,hydrochloric acid, sulfuric acid, ammonium salts, sulfates, andhydrochlorides, etc., are required, and a large quantity of mixed wastewater that contains ammonium, sodium sulfate, sodium chloride andaluminosilicate is produced. For such waste water, a common practice inthe prior art is to adjust the pH to a range of 6-9 and remove themajority of suspended substances first, then remove ammonium ionsthrough a biochemical process, air stripping process or steam strippingprocess, adjust the pH of the obtained salt-containing waste water,remove the majority of suspended substances, decrease the hardness,remove silica and a part of organic substances from the salt-containingwaste water, remove the majority of organic substances through ozonebiological activated carbon adsorption and oxidization or other advancedoxidization processes, further decrease the hardness in an ion exchangeapparatus, concentrate in a concentration apparatus (e.g., reverseosmosis and/or electrodialysis apparatus), and then crystallize by MVRevaporating crystallization or multi-effect evaporation, to obtain mixedsalts of sodium sulfate and sodium chloride that contain some ammoniumsalt; or adjust the pH to a range of 6.5-7.5 and remove the majority ofsuspended substances first, then decrease the hardness, remove silicaand a part of organic substances, remove the majority of organicsubstances through ozone biological activated carbon adsorption andoxidization or other advanced oxidization processes, further decreasethe hardness in an ion exchange apparatus, concentrate in aconcentration apparatus (e.g., reverse osmosis and/or electrodialysisapparatus), and then crystallize by MVR evaporating crystallization ormulti-effect evaporation, to obtain mixed salts of sodium sulfate andsodium chloride that contain some ammonium salts. However, at present,it is difficult to treat the mixed salts that contain ammonium, or thetreatment cost is very high; in addition, the waste water treatment costis increased additionally owing to the ammonium ion removal process inthe early stage.

Besides, the biochemical ammonia removal process can only deal withwaste water with low ammonium content; moreover, the catalyst wastewater can't be treated directly by biochemical treatment because the CODcontent in it is not enough; instead, additional organic substances,such as glucose or starch, etc. have to be added in the biochemicaltreatment process to treat ammoniacal nitrogen through the biochemicaltreatment process. The most critical problem is that the total nitrogenconstant in the waste water treated through a biochemical ammoniaremoval process often doesn't meet the standard (the contents of nitrateions and nitrite ions are out of specification), and additional advancedtreatment is required; in addition, since the salt content in the wastewater is not decreased (20 g/L-30 g/L), the waste water can't bedirectly discharged, and further desalting treatment is required.

To remove ammoniacal nitrogen in the waste water treated through an airstripping ammonia removal process, a large quantity of alkali has to beadded to adjust the pH, and the alkali consumption is heavy; since thealkali in the waste water after ammonia removal can't be recovered, thepH of the treated waste water is very high, quantities of alkalinesubstance is wasted, and the treatment cost is very high; moreover,since the COD content in the catalyst waste water treated through theair stripping process has little change, the salt content in the wastewater is not decreased (20 g/L-30 g/L), the pH is very high, the wastewater can't be directly discharged, further desalting treatment isrequired.

SUMMARY OF THE INVENTION

To overcome the drawbacks in the prior art, i.e., the treatment cost ofwaste water that contains NH₄ ⁺, SO₄ ²⁻, Cl⁻ and Na⁺ is very high, andonly mixed salt crystals can be obtained, the present invention providesa low-cost and environment-friendly treatment apparatus and method ofwater waste that contains NH₄ ⁺, SO₄ ²⁻, Cl⁻ and Na⁺. The apparatus andmethod can be used to recover ammonium, sodium sulfate, and sodiumchloride from the waste water respectively, and thereby the resources inthe waste water can be reused as far as possible.

To attain the object described above, in a first aspect, the presentinvention provides a waste water treatment apparatus for treating wastewater containing ammonium salts, which comprises: a coolingcrystallization unit, a first solid-liquid separation unit, a pHadjustment unit, a first evaporation unit, and a second solid-liquidseparation unit, which are connected sequentially,

wherein the cooling crystallization unit is configured to treat thewaste water by cooling crystallization, to obtain crystal-containingcrystalline solution;the first solid-liquid separation unit is configured to treat thecrystal-containing crystalline solution by first solid-liquidseparation;the pH adjustment unit is configured to adjust the pH of the waste waterbefore evaporation is executed;the first evaporation unit is configured to treat the liquid phaseobtained in the first solid-liquid separation unit by first evaporation,to obtain first ammonia-containing vapor and first crystal-containingconcentrated solution;the second solid-liquid separation unit is configured to treat the firstcrystal-containing concentrated solution by second solid-liquidseparation.

In a second aspect, the present invention provides a waste watertreatment apparatus for treating waste water containing ammonium salts,which comprises: a pH adjustment unit, a second evaporation unit, athird solid-liquid separation unit, a cooling crystallization unit, afirst solid-liquid separation unit, a first evaporation unit, and asecond solid-liquid separation unit, which are connected sequentially,

the pH adjustment unit is configured to adjust the pH of the waste waterbefore evaporation is executed;the second evaporation unit is configured to treat the waste water bysecond evaporation, to obtain second ammonia-containing vapor and secondcrystal-containing concentrated solution;the third solid-liquid separation unit is configured to treat the secondcrystal-containing concentrated solution by third solid-liquidseparation;the cooling crystallization unit is configured to treat the liquid phaseobtained in the third solid-liquid separation by coolingcrystallization, to obtain crystal-containing crystalline solution;the first solid-liquid separation unit is configured to treat thecrystal-containing crystalline solution by first solid-liquidseparation;the first evaporation unit is configured to treat the liquid phaseobtained in the first solid-liquid separation unit by first evaporation,to obtain first ammonia-containing vapor and first crystal-containingconcentrated solution;the second solid-liquid separation unit is configured to treat the firstcrystal-containing concentrated solution by second solid-liquidseparation.

In a third aspect, the present invention provides a waste watertreatment apparatus for treating waste water containing ammonium salts,which comprises: a pH adjustment unit, a first evaporation unit, a firstsolid-liquid separation unit, a cooling crystallization unit, and asecond solid-liquid separation unit, which are connected sequentially,

wherein the pH adjustment unit is configured to adjust the pH of thewaste water before evaporation is executed;the first evaporation unit is configured to treat the waste water byfirst evaporation, to obtain first ammonia-containing vapor and firstcrystal-containing concentrated solution;the first solid-liquid separation unit is configured to treat the firstcrystal-containing concentrated solution by first solid-liquidseparation;the cooling crystallization unit is configured to treat the liquid phaseobtained in the first solid-liquid separation unit by coolingcrystallization, to obtain crystal-containing crystalline solution;the second solid-liquid separation unit is configured to treat thecrystal-containing crystalline solution by second solid-liquidseparation.

In a fourth aspect, the present invention provides a method for treatingwaste water containing ammonium salts that contains NH₄ ⁺, SO₄ ²⁻, Cl⁻and Na⁺, which comprises the following steps:

1) treating waste water to be treated by cooling crystallization toobtain crystalline solution that contains sodium sulfate crystal,wherein the waste water to be treated contains the waste watercontaining ammonium salts;2) treating the crystalline solution that contains sodium sulfatecrystal by first solid-liquid separation, and treating the liquid phaseobtained in the first solid-liquid separation by first evaporation, toobtain first ammonia-containing vapor and first concentrated solutionthat contains sodium chloride crystal;3) treating the first concentrated solution that contains sodiumchloride crystal by second solid-liquid separation;wherein the pH of the waste water to be treated is adjusted to a valuegreater than 7, before the waste water to be treated is treated by thecooling crystallization; in the waste water to be treated, theconcentration of SO₄ ²⁻ is 0.01 mol/L or higher, and the concentrationof Cl⁻ is 5.2 mol/L or lower.

In a fifth aspect, the present invention provides a method for treatingwaste water containing ammonium salts that contains NH₄ ⁺, SO₄ ²⁻, Cl⁻and Na⁺, which comprises the following steps:

1) treating waste water to be treated by second evaporation, to obtainsecond ammonia-containing vapor and second concentrated solution thatcontains sodium sulfate crystal, wherein the waste water to be treatedcontains the waste water containing ammonium salts;2) treating the second concentrated solution that contains sodiumsulfate crystal by third solid-liquid separation, and treating theliquid phase obtained in the third solid-liquid separation by coolingcrystallization, to obtain crystalline solution that contains sodiumsulfate crystal;3) treating the crystalline solution that contains sodium sulfatecrystal by fourth solid-liquid separation, and treating the liquid phaseobtained in the fourth solid-liquid separation by third evaporation, toobtain third ammonia-containing vapor and third concentrated solutionthat contains sodium chloride crystal;4) treating the third concentrated solution that contains sodiumchloride crystal by fifth solid-liquid separation;wherein the pH of the waste water to be treated is adjusted to a valuegreater than 9, before the waste water to be treated is treated by thesecond evaporation; in relation to 1 mol SO₄ ²⁻ contained in the wastewater to be treated, the Cl⁻ contained in the waste water to be treatedis 14 mol or less; the second evaporation is executed in a way that nosodium chloride crystallizes and precipitates.

In a sixth aspect, the present invention provides a method for treatingwaste water containing ammonium salts that contains NH₄ ⁺, SO₄ ²⁻, Cl⁻and Na⁺, which comprises the following steps:

1) treating waste water to be treated by fourth evaporation, to obtainfourth ammonia-containing vapor and fourth concentrated solution thatcontains sodium chloride crystal, wherein the waste water to be treatedcontains the waste water containing ammonium salts;2) treating the fourth concentrated solution that contains sodiumchloride crystal by sixth solid-liquid separation, and treating theliquid phase obtained in the sixth solid-liquid separation by coolingcrystallization, to obtain crystalline solution that contains sodiumsulfate crystal;3) treating the concentrated solution that contains sodium sulfatecrystal by seventh solid-liquid separation;wherein the pH of the waste water to be treated is adjusted to a valueequal to or greater than 9, before the waste water to be treated istreated by the fourth evaporation; in relation to 1 mol SO₄ ²⁻ containedin the waste water to be treated, the Cl⁻ contained in the waste waterto be treated is 7.15 mol or more;the cooling crystallization is executed in a way that no sodium chloridecrystallizes and precipitates.

With the technical scheme described above, for waste water containingammonium salts, which contains NH₄ ⁺, SO₄ ²⁻, Cl⁻ and Na⁺, first, sodiumsulfate crystal is obtained through cooling crystallization andsolid-liquid separation, then the pH value of the liquid phase obtainedin the solid-liquid separation is adjusted to a specific range, and thensodium chloride crystal and first ammonia water are obtained by firstevaporation; alternatively, the pH value of the waste water to betreated is adjusted to a specific range in advance, then sodium chloridecrystal and ammonia water are obtained by fourth evaporation, theconcentration of chloride ions in the sixth mother liquid subject tocooling crystallization is controlled, and then sodium sulfate crystalis obtained through solid-liquid separation by means of coolingcrystallization. With the method, high-purity sodium sulfate and sodiumchloride can be obtained respectively, difficulties in mixed salttreatment and reuse can be avoided, the ammonia and salt separationprocess is accomplished at the same time, the temperature of the wastewater is increased and the temperature of the ammonia-containing vaporis decreased at the same time through heat exchange, and thereby acondenser is not required, the heat in the evaporation process isutilized reasonably, energy is saved, the waste water treatment cost isreduced, the ammonium in the waste water is recovered in the form ofammonia water, the sodium chloride and sodium sulfate are recovered inthe form of crystal respectively, no waste residue or waste liquid isproduced in the entire process, and a purpose of changing wastes intovaluables is achieved.

Furthermore, by utilizing evaporation and cooling treatment incombination, the method improves the concentration ratio of evaporationand the efficiency of evaporation, reduces the quantity of circulatingliquid in the treatment system, and attains an energy-saving effect aswell. By cooling crystallization, the content of sodium sulfate in themother liquid for producing sodium sulfate is greatly decreased, and theefficiency of evaporation for sodium chloride production is improved;besides, before the liquid phase obtained in the sixth solid-liquidseparation is treated by cooling crystallization, preferably theconcentration of Cl⁻ in the liquid phase is adjusted with the wastewater containing ammonium salts and sodium sulfate crystal eluent toavoid precipitation of sodium chloride in the cooling crystallizationprocess and thereby improve the precipitation ratio of sodium sulfate inthe cooling crystallization process.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic structural diagram of the waste water treatmentapparatus in an embodiment of the present invention;

FIG. 2 is a schematic structural diagram of the waste water treatmentapparatus in another embodiment of the present invention;

FIG. 3 is a schematic structural diagram of the waste water treatmentapparatus in another embodiment of the present invention;

FIG. 4 is a flow diagram of the method for treating waste watercontaining ammonium salts in an embodiments of the present invention.

FIG. 5 is a flow diagrams of the method for treating waste watercontaining ammonium salts in another embodiments of the presentinvention.

FIG. 6 is a flow diagram of the method for treating waste watercontaining ammonium salts in another embodiments of the presentinvention.

FIG. 7 is a flow diagram of the method for treating waste watercontaining ammonium salts in another embodiments of the presentinvention.

FIG. 8 is a flow diagram of the method for treating waste watercontaining ammonium salts in another embodiments of the presentinvention.

FIG. 9 is a flow diagram of the method for treating waste watercontaining ammonium salts in another embodiments of the presentinvention

Brief Description of the Symbols 1 - first MVR evaporation device 53 -first mother liquid tank 2 - cooling crystallization device 54 - secondmother liquid tank 3 - second MVR evaporation device 61 - first pHmeasuring device 22, 55 - low temperature treatment 62 - second pHmeasuring device tank 31 - first heat exchange device 63 - third pHmeasuring device 32 - second heat exchange device 70 - eleventhcirculation pump 33 - third heat exchange device 71 - first circulationpump 34 - fourth heat exchange device 72 - second circulation pump 35 -fifth heat exchange device 73 - third circulation pump 36 - sixth heatexchange device 74 - fourth circulation pump 38 - eighth heat exchangedevice 75 - fifth circulation pump 30 - eleventh heat exchange device76 - sixth circulation pump 50 - third mother liquid tank 77 - seventhcirculation pump 51 - first ammonia water storage tank 78 - eighthcirculation pump 52 - second ammonia water storage 79 - ninthcirculation pump tank 80 - tenth circulation pump 81 - vacuum pump 82 -circulating water tank 83 - tail gas absorption tower 84 - fourteenthcirculation pump 9 - concentration device 91 - first solid-liquidseparation device 92 - second solid-liquid separation device 101, 102 -compressor

DETAILED DESCRIPTION OF THE EMBODIMENTS

The ends points and any value in the ranges disclosed in the presentinvention are not limited to the exact ranges or values; instead, thoseranges or values shall be comprehended as encompassing values that areclose to those ranges or values. For numeric ranges, the end points ofthe ranges, the end points of the ranges and the discrete point values,and the discrete point values may be combined to obtain one or more newnumeric ranges, which shall be deemed as having been disclosedspecifically in this document.

Hereunder the present invention will be detailed with reference to FIGS.1-9, but the present invention is not limited to FIGS. 1-9.

In a first aspect, the present invention provides a waste watertreatment apparatus for treating waste water containing ammonium salts,as shown in FIG. 1, which comprises: a cooling crystallization unit, afirst solid-liquid separation unit, a pH adjustment unit, a firstevaporation unit, and a second solid-liquid separation unit, which areconnected sequentially,

wherein the cooling crystallization unit is configured to treat thewaste water by cooling crystallization, to obtain crystal-containingcrystalline solution;the first solid-liquid separation unit is configured to treat thecrystal-containing crystalline solution by first solid-liquidseparation;the pH adjustment unit is configured to adjust the pH of the waste waterbefore evaporation is executed;the first evaporation unit is configured to treat the liquid phaseobtained in the first solid-liquid separation unit by first evaporation,to obtain first ammonia-containing vapor and first crystal-containingconcentrated solution;the second solid-liquid separation unit is configured to treat the firstcrystal-containing concentrated solution by second solid-liquidseparation.

According to a preferred embodiment of the present invention, the wastewater treatment apparatus further comprises a low-temperature treatmentunit arranged between the first evaporation unit and the secondsolid-liquid separation unit and configured to treat the concentratedsolution obtained in the first evaporation unit by low temperaturetreatment to obtain treated solution. By providing the low-temperaturetreatment unit, the evaporation process in the first evaporation unitcan be used in combination with low temperature treatment, so that theevaporation process in the first evaporation unit may be executed at ahigher temperature, and thereby the solid content in the concentratedsolution obtained in the first evaporation and the efficiency ofevaporation can be improved, and an energy-saving effect can be attainedat the same time.

Any conventional cooling device in the art may be used as thelow-temperature treatment unit. For example, the low-temperaturetreatment unit may be a low temperature treatment tank 55. Preferably,the low temperature treatment tank 55 may be equipped with a coolingcomponent in it; specifically, the cooling component may be a componentthat introduces cooling water. With the cooling component, the firstconcentrated solution in the low temperature treatment tank can becooled quickly.

Preferably, the low temperature treatment tank 55 may be equipped with astirring component in it. Under the stirring action of the stirringcomponent, the solid phase and liquid phase distribution and thetemperature distribution in the first concentrated solution are uniform,and a purpose that the sodium sulfate crystal is dissolved fully and thesodium chloride crystal precipitates as far as possible is attained.

Preferably, the waste water treatment apparatus further comprises apipeline configured to return the liquid phase obtained in the secondsolid-liquid separation unit to the cooling crystallization unit.

According to the present invention, there is no particular restrictionon the evaporation device used in the evaporation process, as long asthe evaporation device can accomplish evaporation. For example, thefirst evaporation unit may be selected from one or more of MVRevaporation device, single-effect evaporation device, multi-effectevaporation device, and flash evaporation device respectively.Preferably, the first evaporation unit is a MVR evaporation device.

The MVR evaporation device may be selected from one or more of MVRfalling film evaporator, MVR forced circulation evaporator, MVR-FCcontinuous crystallizing evaporator, and MVR-OSLO continuouscrystallizing evaporator. Wherein the MVR evaporation device preferablyis a MVR forced circulation evaporator or MVR-FC continuouscrystallizing evaporator, more preferably is a two-stage MVR evaporatingcrystallizer that incorporates falling film and forced circulation.

The single-effect evaporation device or the evaporators in themulti-effect evaporation device may be selected from one or more offalling-film evaporator, rising-film evaporator, scraped evaporator,central circulation tube evaporator, basket evaporator, external heatingevaporator, forced circulation evaporator, and Levin evaporator, forexample. Wherein the evaporators preferably are forced circulationevaporators or external heating evaporators. Each of the aboveevaporators consists of a heating chamber and an evaporation chamber,and may include other auxiliary evaporation components as required, suchas froth separator configured to further separate liquid and froth,condenser configured to condense the secondary steam fully, and vacuumdevice for depressurization, etc. In the case that the evaporationdevice is a multi-effect evaporation device, there is no particularrestriction on the number of evaporators included in the multi-effectevaporation device; in other words, the number of evaporators includedin the multi-effect evaporation device may be selected according to theevaporation conditions as required, and may be 2 or more, preferably is2-5, more preferably is 2-4.

The flash evaporation device may be single-stage flash evaporationdevice or multistage flash evaporation device. The single-stage flashevaporation device or the evaporators in the multistage flashevaporation device may be selected from one or more of thin-film flashevaporator, high-efficiency vapor-liquid flash evaporator, rotary flashevaporator, for example. Wherein the evaporators preferably arethin-film flash evaporator, high-efficiency vapor-liquid flashevaporator. In the case that the evaporation device is a multistageflash evaporation device, the number of evaporators included in themultistage flash evaporation device may be 2 or more, preferably is 2-4.

According to the present invention, there is no particular restrictionon the cooling crystallization unit, as long as it can accomplishcooling crystallization. For example, a continuous cooling crystallizerequipped with an external cooling heat exchanger may be used, or acrystallization tank with a cooling component (e.g., coolingcrystallization device 2) may be used. The cooling component may coolthe waste water to be treated in the cooling crystallization device to acondition required for cooling crystallization by introducing a coolingmedium. Preferably a mixing component (e.g., a stirrer, etc.) isprovided in the cooling crystallization device to mix the waste water tobe treated homogeneously and attain a uniform cooling effect, so thatthe sodium sulfate in the waste water to be treated can precipitatefully and the grain size can be increased. The cooling crystallizationdevice is preferably equipped with a circulation pump. To avoid thegeneration of a large quantity of fine crystal nuclei and prevent thegeneration of a large quantity of secondary crystal nuclei incurred byhigh-speed collision between the crystal grains in the circulatingcrystal slurry and the impeller, the circulation pump preferably is alow-speed centrifugal pump, more preferably is a high-flow low-speedinduced flow pump impeller or high-flow, low lift and low-speed axialpump.

According to the present invention, there is no particular restrictionon the first solid-liquid separation unit and the second solid-liquidseparation unit, as long as they can attain a solid-liquid separationeffect. For example, they can be selected from one or more ofcentrifugation device, filtering device, and sedimentation devicerespectively. For the purpose of improving the solid-liquid separationefficiency, preferably, both of the first solid-liquid separation unitand the second solid-liquid separation unit are centrifugation devices.

According to the present invention, there is no particular restrictionon the pH adjustment unit, as long as it can adjust the pH of the wastewater to be treated to the specified range. For example, the pHadjustment unit may be a pH adjustor (pH adjustment reagent)introduction device. NaOH may be used as the pH adjustor, for example.Specifically, NaOH solution may be added into the waste water to betreated to accomplish pH adjustment. To monitor the pH after theadjustment, the device may further comprise a pH measuring device, whichmay be any pH meter in the art.

In a second aspect, the present invention provides a waste watertreatment apparatus for treating waste water containing ammonium salts,as shown in FIG. 3, which comprises: a pH adjustment unit, a secondevaporation unit, a third solid-liquid separation unit, a coolingcrystallization unit, a first solid-liquid separation unit, a firstevaporation unit, and a second solid-liquid separation unit, which areconnected sequentially,

wherein the pH adjustment unit is configured to adjust the pH of thewaste water before evaporation is executed;the second evaporation unit is configured to treat the waste water bysecond evaporation, to obtain second ammonia-containing vapor and secondcrystal-containing concentrated solution;the third solid-liquid separation unit is configured to treat the secondcrystal-containing concentrated solution by third solid-liquidseparation;the cooling crystallization unit is configured to treat the liquid phaseobtained in the third solid-liquid separation by coolingcrystallization, to obtain crystal-containing crystalline solution;the first solid-liquid separation unit is configured to treat thecrystal-containing crystalline solution by first solid-liquidseparation;the first evaporation unit is configured to treat the liquid phaseobtained in the first solid-liquid separation unit by first evaporation,to obtain first ammonia-containing vapor and first crystal-containingconcentrated solution;the second solid-liquid separation unit is configured to treat the firstcrystal-containing concentrated solution by second solid-liquidseparation.preferably, the waste water treatment apparatus further comprises apipeline configured to return the liquid phase obtained in the secondsolid-liquid separation unit to the second evaporation unit.

According to a preferred embodiment of the present invention, the wastewater treatment apparatus further comprises a low-temperature treatmentunit arranged between the first evaporation unit and the secondsolid-liquid separation unit and configured to treat the concentratedsolution obtained in the first evaporation unit by low temperaturetreatment to obtain treated solution. By providing the low-temperaturetreatment unit, the evaporation process in the first evaporation unitcan be used in combination with low temperature treatment, so that theevaporation process in the first evaporation unit may be executed at ahigher temperature, and thereby the solid content in the concentratedsolution obtained in the first evaporation and the efficiency ofevaporation can be improved, and an energy-saving effect can be attainedat the same time.

Here, the evaporation unit, the cooling crystallization unit, thesolid-liquid separation unit, the pH adjustment unit, and thelow-temperature treatment unit are the same as those in the firstaspect.

In a third aspect, the present invention provides a waste watertreatment apparatus for treating waste water containing ammonium salts,as shown in FIG. 2, which comprises: a pH adjustment unit, a firstevaporation unit, a first solid-liquid separation unit, a coolingcrystallization unit, and a second solid-liquid separation unit, whichare connected sequentially,

wherein the pH adjustment unit is configured to adjust the pH of thewaste water before evaporation is executed;the first evaporation unit is configured to treat the waste water byfirst evaporation, to obtain first ammonia-containing vapor and firstcrystal-containing concentrated solution;the first solid-liquid separation unit is configured to treat the firstcrystal-containing concentrated solution by first solid-liquidseparation;the cooling crystallization unit is configured to treat the liquid phaseobtained in the first solid-liquid separation unit by coolingcrystallization, to obtain crystal-containing crystalline solution;the second solid-liquid separation unit is configured to treat thecrystal-containing crystalline solution by second solid-liquidseparation.

According to a preferred embodiment of the present invention, the wastewater treatment apparatus further comprises a low-temperature treatmentunit arranged between the first evaporation unit and the firstsolid-liquid separation unit and configured to treat the concentratedsolution obtained in the first evaporation unit by low temperaturetreatment to obtain treated solution. By providing the low-temperaturetreatment unit, the evaporation process in the first evaporation unitcan be used in combination with low temperature treatment, so that theevaporation process in the first evaporation unit may be executed at ahigher temperature, and thereby the solid content in the concentratedsolution obtained in the first evaporation and the efficiency ofevaporation can be improved, and an energy-saving effect can be attainedat the same time.

Preferably, the waste water treatment apparatus further comprises apipeline configured to return the liquid phase obtained in the secondsolid-liquid separation unit to the first evaporation unit.

Here, the evaporation unit, the cooling crystallization unit, thesolid-liquid separation unit, and the pH adjustment unit are the same asthose in the first aspect.

According to the present invention, the devices described above may beused in the waste water treatment method in the present invention.According to the waste water treatment apparatus for treating wastewater containing ammonium salts, preferably, the apparatus does notcomprise separate non-evaporation deamination device (device only forremoving ammonia from waste water, such as biochemical treatment device,deamination membrane and the like), and high-purity ammonia water,sodium sulfate crystals and sodium chloride crystals can be separatedfrom the waste water containing NH₄ ⁺, SO₄ ²⁻, Cl⁻ and Na⁺ only by thecombination of the evaporation unit and the solid-liquid separationunit.

In the present invention, the waste water treatment apparatus mayfurther comprise heat exchange devices, such as heat exchangers, etc.There is no particular restriction on the quantity and positions of theheat exchange devices. For example, the heat exchange devices may be thefourth heat exchange device 34 and the third heat exchange device 33 inthe FIG. 4 for cooling the first ammonia-containing vapor and heatingthe liquid phase obtained in the first solid-liquid separation unit, andthe second heat exchange device 32 and the sixth heat exchange device 36for heating the waste water to be treated. According to the presentinvention, the waste water treatment apparatus further comprises a tailgas absorption unit configured to absorb ammonia in the tail gas fromthe waste water treatment apparatus. A tail gas absorption tower 83 maybe used as the tail gas absorption unit. There is no particularrestriction on the tail gas absorption tower 83; in other words, thetail gas absorption tower 83 may be any conventional absorption tower inthe art, such as plate-type absorption tower, packed absorption tower,falling film absorption tower, or void tower, etc. The tail gasabsorption tower 83 may be used in combination with a fourth circulationpump 74 which is configured to drive the circulating water to circulatein the tail gas absorption tower 83. The tail gas absorption tower 83may further be used in combination with a circulating water tank 82; forexample, water may be replenished with a third circulation pump 73 fromthe circulating water tank 82 to the tail gays absorption tower 83;fresh water may be replenished to the circulating water tank 82, andthereby the temperature and ammonia content of the service water of thevacuum pump 81 may be decreased at the same time.

In the present invention, it should be understood that theammonia-containing vapors are secondary steam generally referred in theart. All the pressure values are gauge pressure values.

In a fourth aspect, the present invention provides a method for treatingwaste water containing ammonium salts that contains NH₄ ⁺, SO₄ ²⁻, Cl⁻and Na⁺ as shown in FIGS. 4-5, which comprises the following steps:

1) treating waste water to be treated by cooling crystallization toobtain crystalline solution that contains sodium sulfate crystal,wherein the waste water to be treated contains the waste watercontaining ammonium salts;2) treating the crystalline solution that contains sodium sulfatecrystal by first solid-liquid separation, and treating the liquid phaseobtained in the first solid-liquid separation by first evaporation, toobtain first ammonia-containing vapor and first concentrated solutionthat contains sodium chloride crystal;3) treating the first concentrated solution that contains sodiumchloride crystal by second solid-liquid separation;wherein the pH of the waste water to be treated is adjusted to a valuegreater than 7, before the waste water to be treated is treated by thecooling crystallization; in the waste water to be treated, theconcentration of SO₄ ²⁻ is 0.01 mol/L or higher, and the concentrationof Cl⁻ is 5.2 mol/L or lower.

Preferably, the waste water to be treated is the waste water containingammonium salts; or the waste water to be treated contains the wastewater containing ammonium salts and the liquid phase obtained in thesecond solid-liquid separation.

More preferably, the waste water to be treated is mixed solution of thewaste water containing ammonium salts and at least a part of the liquidphase obtained in the second solid-liquid separation.

The method provided in the present invention can treat waste watercontaining ammonium salts, which contains NH₄ ⁺, SO₄ ²⁻, Cl⁻ and Na⁺,and there is no particular restriction on the waste water containingammonium salts, except that the waste water contains NH₄ ⁺, SO₄ ²⁻, Cl⁻and Na⁺. For the purpose of improving the waste water treatmentefficiency, the concentration of SO₄ ²⁻ contained in the waste water tobe treated is 0.01 mol/L or higher, more preferably is 0.07 mol/L orhigher, further preferably is 0.1 mol/L or higher, still furtherpreferably is 0.2 mol/L or higher, particularly preferably is 0.3 mol/Lor higher, e.g., 0.4-1 mol/L. In addition, the concentration of Cl⁻ inthe waste water to be treated is 5.2 mol/L or lower, preferably is 4.5mol/L or lower, more preferably is 3 mol/L or lower, e.g., 1.5-3 mol/L.By controlling the concentration values of SO₄ ²⁻ and Cl⁻ within theabove-mentioned ranges, sodium sulfate precipitates but sodium chloridehardly precipitates in the cooling crystallization, and thereby apurpose of separating sodium sulfate efficiently is attained.

Examples of the content of SO₄ ²⁻ in the waste water to be treated mayinclude: 0.0 mol/L, 0.03 mol/L, 0.05 mol/L, 0.08 mol/L, 0.1 mol/L, 0.2mol/L, 0.3 mol/L, 0.4 mol/L, 0.5 mol/L, 0.6 mol/L, 0.7 mol/L, 0.8 mol/L,0.9 mol/L, 1 mol/L, 1.1 mol/L, 1.2 mol/L, 1.3 mol/L, 1.4 mol/L, or 1.5mol/L, etc.

Examples of the content of Cl⁻ in the waste water to be treated mayinclude: 0.01 mol/L, 0.05 mol/L, 0.1 mol/L, 0.3 mol/L, 0.6 mol/L, 0.8mol/L, 1 mol/L, 1.2 mol/L, 1.4 mol/L, 1.6 mol/L, 1.8 mol/L, 2.0 mol/L,2.2 mol/L, 2.4 mol/L, 2.6 mol/L, 2.8 mol/L, 3 mol/L, 3.2 mol/L, 3.4mol/L, 3.6 mol/L, 3.8 mol/L, 4 mol/L, 4.5 mol/L, 5 mol/L, or 5.1 mol/L,etc.

In the present invention, there is no particular restriction on theorder of the first heat exchange, the adjustment of pH value of thewaste water to be treated, and the blending process of the waste waterto be treated (in the case that the waste water to be treated containsthe waste water containing ammonium salts and the liquid phase obtainedin the second solid-liquid separation, a blending process of the wastewater to be treated is required); in other words, the order may beselected appropriately as required; for example, these procedures may beaccomplished before the waste water to be treated is treated by coolingcrystallization.

In the present invention, the purpose of the cooling crystallization isto drive the sodium sulfate to precipitate while prevent the sodiumchloride, ammonium chloride, and ammonium sulfate from precipitating, sothat the sodium sulfate can be separated successfully from the wastewater. The cooling crystallization only drives the sodium sulfate toprecipitate, but doesn't exclude sodium chloride and other substances,which are entrained in the sodium sulfate crystal or absorbed to thesurface of the sodium sulfate crystal. In the present invention,preferably the content of sodium sulfate in the obtained sodium sulfatecrystal is 92 mass % or higher, more preferably is 96 mass % or higher,further preferably is 98 mass % or higher. It should be understood thatthe quantity of the obtained sodium sulfate crystal is measured by drymass. If the content of sodium sulfate in the obtained sodium sulfatecrystal is within the above-mentioned range, it is deemed that onlysodium sulfate precipitates.

In the present invention, there is no particular restriction on theconditions of the cooling crystallization; in other words, theconditions may be selected appropriately as required, as long as aneffect of separation and crystallization of the sodium sulfate isattained. The conditions of the cooling crystallization may include:temperature: −21.7° C.-17.5° C., preferably −20° C.-5° C., morepreferably −10° C.-5° C., further preferably −10° C.-0° C., particularlypreferably −4° C.-0° C.; time (e.g., measured as the retention time inthe cooling crystallization device 2): 5 min. or more, preferably 60min.-180 min., more preferably 90 min.-150 min., further preferably 120min.-150 min., or 130 min.-150 min., or 120 min.-130 min. By controllingthe conditions of the cooling crystallization within the above-mentionedranges, the sodium sulfate can precipitate fully.

Examples of the temperature of the cooling crystallization may include:−21° C., −20° C., −19° C., −18° C., −17° C., −16° C., −15° C., −14° C.,−13° C., −12° C., −11° C., −10° C., −9° C., −8° C., −7° C., −6° C., −5°C., −4° C., −3° C., −2° C., −1° C., or 0° C., etc.

Examples of the time of the cooling crystallization may include: 5 min.,6 min., 7 min., 8 min., 10 min., 15 min., 20 min., 25 min., 30 min., 35min., 40 min., 45 min., 50 min., 52 min., 54 min., 56 min., 58 min., 60min., 65 min., 70 min., 75 min., 80 min., 85 min., 90 min., 95 min., 100min., 105 min., 110 min., 115 min., 120 min., 130 min., 140 min., 150min., or 160 min.

According to the present invention, there is no particular restrictionon the method of cooling crystallization. For example, the coolingcrystallization may be executed continuously or in batch, as long as thepurpose of cooling the waste water to be treated and driving the sodiumsulfate to crystallize and precipitate is attained. Preferably, thecooling crystallization is executed continuously. The coolingcrystallization of sodium sulfate may be executed in any conventionalcooling crystallization apparatus in the art. For example, the coolingcrystallization may be executed in a continuous cooling crystallizerequipped with an external cooling heat exchanger or in a crystallizationtank with a cooling component (i.e., the cooling crystallization device2). The cooling component may cool the waste water to be treated in thecooling crystallization device to a condition required for coolingcrystallization by introducing a cooling medium. Preferably a mixingcomponent (e.g., a stirrer, etc.) is provided in the coolingcrystallization device to mix the waste water to be treatedhomogeneously and attain a uniform cooling effect, so that the sodiumsulfate in the waste water to be treated can precipitate fully and thegrain size can be increased. The cooling crystallization device ispreferably equipped with a circulation pump. To avoid the generation ofa large quantity of fine crystal nuclei and prevent the generation of alarge quantity of secondary crystal nuclei incurred by high-speedcollision between the crystal grains in the circulating crystal slurryand the impeller, the circulation pump preferably is a low-speedcentrifugal pump, more preferably is a high-flow low-speed induced flowpump impeller or high-flow, low lift and low-speed axial pump.

According to the present invention, the pH of the waste water to betreated is adjusted to a value greater than 7, before the waste water tobe treated is treated by the cooling crystallization. By adjusting thepH value of the waste water to be treated, the majority of NH₄ ⁺ existsin the form of ammonia molecules; thus, ammonium sulfate and/or ammoniumchloride will not precipitate in the cooling crystallization process,and the precipitation ratio of sodium sulfate can be improved.Preferably, the pH value of the waste water to be treated is adjusted to8 or above before the waste water to be treated is treated by coolingcrystallization, so that ammonium sulfate and/or ammonium chloride willnot precipitate in the cooling crystallization process (the content ofammonium salts in the obtained crystal is 1 mass % or lower, preferablyis 0.5 mass % or lower).

In the present invention, there is no particular restriction on the pHadjustment method. For example, the pH value of the waste water to betreated may be adjusted by adding an alkaline substance. There is noparticular restriction on the alkaline substance, as long as thealkaline substance can attain the purpose of adjusting the pH. To avoidintroducing any new impurity into the waste water to be treated andimprove the purity of the obtained crystal, the alkaline substancepreferably is NaOH. In addition, in view that the second mother liquid(i.e., the liquid phase obtained in the second solid-liquid separation)contains NaOH at relatively high concentration, preferably the secondmother liquid is used as the alkaline substance.

The alkaline substance may be added with a conventional method in theart. However, preferably the alkaline substance is mixed in the form ofwater solution with the waste water to be treated. For example, watersolution that contains the alkaline substance may be charged into apipeline through which the waste water to be treated is inputted. Thereis no particular restriction on the content of the alkaline substance inthe water solution, as long as the water solution can attain the purposeof adjusting the pH. However, to reduce the amount of water and furtherreduce the cost, preferably a saturated water solution of the alkalinesubstance or a second mother liquid is used. To monitor the pH of thewaste water to be treated, the pH of the waste water to be treated maybe measured after the pH adjustment.

According to a preferred embodiment of the present invention, thecooling crystallization is executed in the cooling crystallizationdevice 2. Before the waste water to be treated is fed into the coolingcrystallization device 2, the pH value of the waste water to be treatedis adjusted by introducing the water solution that contains the alkalinesubstance into the pipeline through which the waste water to be treatedis to be fed into the cooling crystallization device 2 and mixing thewater solution that contains the alkaline substance with the waste waterto be treated in the pipeline. In addition, the pH value is measuredwith a first pH measuring device 61 after the adjustment.

By controlling the cooling crystallization to proceed at theabove-mentioned temperature and pH, sodium sulfate can precipitate fullywhile sodium chloride, ammonium sulfate and/or ammonium chloride don'tprecipitate in the cooling crystallization process, so that the purposeof separating and purifying sodium sulfate is attained.

In the present invention, to control the grain size distribution of thecrystal in the cooling crystallization device 2 and decrease the contentof fine grains, preferably a part of the liquid after thecrystallization in the cooling crystallization device 2 (i.e., theliquid in the cooling crystallization device 2, hereinafter alsoreferred to as cooled circulating liquid) is mixed with the waste waterto be treated and then returned to the cooling crystallization device 2for further cooling crystallization. For example, the process ofreturning the cooled circulating liquid to the cooling crystallizationdevice 2 for further cooling crystallization may be executed byreturning the cooled circulating liquid with a second circulation pump72 to a position just before the sixth heat exchange device 36, so thatthe cooled circulating liquid is mixed with the waste water to betreated and then enters into the cooling crystallization device 2 againfor further cooling crystallization. The quantity of returned cooledcirculating liquid may be defined by the recirculation ratio of thecooling crystallization, which refers to the ratio of the recirculatedamount to the difference between the total amount of liquid fed into thecooling crystallization device 2 and the recirculated amount. Therecirculation ratio may be set appropriately according to the degree ofsuper-saturation of sodium sulfate in the cooling crystallization device2, to ensure the granularity of sodium sulfate crystal. To control thegrain size distribution of the crystal obtained in the coolingcrystallization and decrease the content of fine grains, preferably thedegree of super-saturation is controlled to be lower than 1.5 g/L, morepreferably is lower than 1 g/L.

To obtain relatively thick first ammonia water and improve the purity ofsodium sulfate obtained in the cooling crystallization and theefficiency of the cooling crystallization, preferably the waste water tobe treated is concentrated to obtain ammonia-containing vapor andconcentrated waste water to be treated before the waste water to betreated is treated by the cooling crystallization. Here, the purpose ofthe concentration is to obtain first ammonia water at relatively highconcentration and control the concentration of the first ammonia watermore easily, and concentrate the waste water to be treated to facilitatethe cooling crystallization. There is no particular restriction on thedegree of the concentration, as long as the concentrated waste water tobe treated meets the above-mentioned cooling crystallizationrequirement. The conditions and equipment of the concentration are thesame as those of the first evaporation. However, preferably thetemperature of the concentration is higher than the temperature of thefirst evaporation, so that the waste water to be treated can be treatedquickly by the first evaporation, and thereby the efficiency of thefirst evaporation can be improved while thick first ammonia water isobtained. Furthermore, the pH value of the waste water to be treated isadjusted to a value greater than 9, more preferably greater than 10.8,before the waste water to be treated is concentrated. Here, preferablythe pH value is adjusted by means of NaOH.

By adjusting the pH value of the waste water to a value greater than 9and concentrating the waste water before the waste water is treated bythe cooling crystallization, first ammonia water at relatively highconcentration can be obtained, the purity of sodium sulfate obtained inthe cooling crystallization can be improved, and the efficiency can beimproved.

In the present invention, through first solid-liquid separation of thecrystalline solution that contains sodium sulfate crystal, sodiumsulfate crystal and first mother liquid (i.e., a liquid phase obtainedin the first solid-liquid separation) are obtained. There is noparticular restriction on the method of the first solid-liquidseparation. For example, the method may be selected from one or more ofcentrifugation, filtering, and sedimentation.

According to the present invention, the first solid-liquid separationmay be executed in a first solid-liquid separation device 91 (e.g.,centrifugal machine, or filter, etc.). After the first solid-liquidseparation, the first mother liquid obtained in the first solid-liquidseparation device 91 is stored temporarily in a first mother liquid tank53, and may be pumped by a sixth circulation pump 76 into the first MVRevaporation device 1 for first evaporation. Besides, it is inevitablethat the obtained sodium sulfate crystal has some impurities absorbedthereon, such as chloride ions, free ammonia, and hydroxyl ions, etc.Preferably, the sodium sulfate crystal is washed in first washing withwater or sodium sulfate solution to remove the absorbed impurities,reduce off-odor of the solid salt, decrease causticity, and improve thepurity of the crystal, and may be dried if anhydrous sodium sulfate isto be obtained.

There is no particular restriction on the specific method for the firstsolid-liquid separation and the first washing. For example, the firstsolid-liquid separation and the first washing may be executed with aconventional solid-liquid separation apparatus in the art, or may beexecuted in a staged solid-liquid separation apparatus, such as a bandfilter. The first washing comprises elutriation and/or elution.

There is no particular restriction on the above-mentioned washing; inother words, the washing may be executed with a conventional method inthe art. There is no particular restriction on the number of cycles ofthe washing. For example, one or more cycles may be used. To obtainsodium sulfate crystal at higher purity, preferably the washing isexecuted for 2-4 cycles. The first washing preferably is executed withsodium sulfate solution (the concentration of the sodium sulfatesolution preferably is the concentration of sodium sulfate in watersolution where both sodium chloride and sodium sulfate are saturated atthe temperature corresponding to the sodium sulfate crystal to bewashed). The liquid produced in the washing preferably is returned tothe cooling crystallization device 2. For example, the liquid may bereturned by means of an eighth circulation pump 78 to the coolingcrystallization device 2.

According to a preferred embodiment of the present invention, after thecrystalline solution that contains sodium sulfate is obtained throughcooling crystallization, solid-liquid separation is executed with asolid-liquid separation device, and the crystal obtained in thesolid-liquid separation is eluted with sodium sulfate solution (theconcentration of the sodium sulfate solution preferably is theconcentration of sodium sulfate in water solution where both sodiumchloride and sodium sulfate are saturated at the temperaturecorresponding to the sodium sulfate crystal to be washed), and theliquid obtained in the elution is returned to the coolingcrystallization device 2. Through the washing process described above,the purity of the obtained sodium sulfate crystal can be improved.

In the present invention, to reduce the cost of the waste watertreatment, the first mother liquid is concentrated after the firstsolid-liquid separation is finished, preferably before the first motherliquid is charged into the first MVR evaporation device 1; preferably,the concentration is executed in a way that no crystal precipitates fromthe liquid phase obtained in the first solid-liquid separation. Theconcentration may be executed with a conventional concentration methodin the art, such as reverse osmosis or electrodialysis, etc. Wherein forthe purpose of reducing the cost and improving the efficiency of thefollow-up first evaporation, the concentration preferably is executedthrough an electrodialysis process; for example, the concentration maybe executed with a concentration device 9 (an electrodialysisapparatus). The thick solution obtained in the electrodialysis processis treated by first evaporation in the next step, while the thinsolution preferably is returned to the concentration step before thetreatment of the waste water containing ammonium salts for furtherconcentration and then treated with the method in the present invention.Through the concentration, the liquid volume in the first evaporationprocess can be reduced, the efficiency of the first evaporation can beimproved, and thereby the efficiency of waste water treatment can beimproved and the cost can be reduced.

According to the present invention, to take full advantage of thecooling capacity of the first mother liquid, preferably first heatexchange between the first mother liquid and the waste water to betreated is executed before the waste water to be treated is treated bycooling crystallization.

According to a preferred embodiment of the present invention, the firstheat exchange is executed in a second heat exchange device 32;specifically, the first mother liquid and the waste water to be treatedflow through the second heat exchange device 32 respectively, so thatthey exchange heat and thereby the temperature of the waste water to betreated is decreased to facilitate cooling crystallization, while thetemperature of the first mother liquid is increased to facilitate firstevaporation. After the first heat exchange in the second heat exchangedevice 32, the temperature of the waste water to be treated is −20.7°C.-16.5° C., preferably is −5° C.-10° C., close to the temperature ofcooling crystallization. According to the present invention, tofacilitate cooling crystallization, preferably first heat exchangebetween the waste water to be treated and refrigerating liquid isexecuted further. According to a preferred embodiment of the presentinvention, the first heat exchange between the waste water to be treatedand the refrigerating liquid is executed in a sixth heat exchange device36; specifically, the refrigerating liquid and the waste water to betreated flow through the sixth heat exchange device 36 respectively sothat they exchange heat with each other, and thereby the temperature ofthe waste water to be treated is decreased to facilitate coolingcrystallization. The refrigerating liquid may be any conventionalrefrigerating liquid for cooling in the art, as long as it can cool thewaste water to be treated to a temperature that meets the coolingcrystallization requirement.

In the present invention, the purpose of the first evaporation is todrive sodium chloride to precipitate or drive sodium chloride and sodiumsulfate to precipitate together, and evaporate ammonia, to attain apurpose of separating the ammonia and salts in the waste water.According to the present invention, by controlling the conditions of thefirst evaporation, sodium chloride precipitates first as the solvent isreduced continuously, and then some sodium sulfate precipitates, so thatfirst concentrated solution that contains sodium chloride crystal isobtained (the first concentrated solution that only contains sodiumchloride crystal or contains sodium chloride crystal and sodium sulfatecrystal).

In the present invention, the first evaporation may be executed in aconventional evaporation device in the art, such as a MVR evaporationdevice, single-effect evaporation device, flash evaporation device, ormulti-effect evaporation device.

The MVR evaporation device may be selected from one or more of MVRfalling film evaporator, MVR forced circulation evaporator, MVR-FCcontinuous crystallizing evaporator, and MVR-OSLO continuouscrystallizing evaporator. Wherein the MVR evaporation device preferablyis a MVR forced circulation evaporator or MVR-FC continuouscrystallizing evaporator, more preferably is a two-stage MVR evaporatingcrystallizer that incorporates falling film and forced circulation.

The single-effect evaporation device or the evaporators in themulti-effect evaporation device may be selected from one or more offalling-film evaporator, rising-film evaporator, scraped evaporator,central circulation tube evaporator, basket evaporator, external heatingevaporator, forced circulation evaporator, and Levin evaporator, forexample. Wherein the evaporators preferably are forced circulationevaporators or external heating evaporators. Each of the aboveevaporators consists of a heating chamber and an evaporation chamber,and may include other auxiliary evaporation components as required, suchas froth separator configured to further separate liquid and froth,condenser configured to condense the secondary steam fully, and vacuumdevice for depressurization, etc. In the case that the evaporationdevice is a multi-effect evaporation device, there is no particularrestriction on the number of the evaporators included in themulti-effect evaporation device; preferably 2 or more evaporators areused, more preferably 3-5 evaporators are used. According to a preferredembodiment of the present invention, the first evaporation is executedin a first MVR evaporation device 1.

The flash evaporation device may be single-stage flash evaporationdevice or multistage flash evaporation device. The single-stage flashevaporation device or the evaporators in the multistage flashevaporation device may be selected from one or more of thin-film flashevaporator, high-efficiency vapor-liquid flash evaporator, rotary flashevaporator, for example. Wherein the evaporators preferably arethin-film flash evaporator and high-efficiency vapor-liquid flashevaporator. In the case that the evaporation device is a multistageflash evaporation device, the number of evaporators included in themultistage flash evaporation device may be 2 or more, preferably is 2-4.

In the present invention, there is no particular restriction on theevaporation conditions of the first evaporation; in other words, theevaporation conditions may be selected appropriately as required, aslong as the purpose of crystallization can be attained. To improve theefficiency of the first evaporation, the conditions of the firstevaporation may include: temperature: 35° C. or above; pressure: −98 kPaor above; preferably, the conditions of the first evaporation include:temperature: 45° C.-175° C.; pressure: −95 kPa-653 kPa; preferably, theconditions of the first evaporation include: temperature: 60° C.-175°C.; pressure: −87 kPa-653 kPa; preferably, the conditions of the firstevaporation include: temperature: 75° C.-175° C.; pressure: −73 kPa-653kPa; preferably, the conditions of the first evaporation include:temperature: 80° C.-130° C.; pressure: −66 kPa-117 kPa; preferably, theconditions of the first evaporation include: temperature: 95° C.-110°C.; pressure: −37 kPa-12 kPa; preferably, the conditions of the firstevaporation include: temperature: 105° C.-110° C.; pressure: −8 kPa-12kPa.

If a multi-effect evaporation device is used for the first evaporation,in the case of co-current feeding or counter-current feeding, theconditions of the first evaporation refer to the evaporation conditionsin the last evaporator of the multi-effect evaporation device; in thecase of parallel-current feeding, the conditions of the firstevaporation include the evaporation conditions in each evaporator in themulti-effect evaporation device. In addition, to take full advantage ofthe heat in the first evaporation process, preferably the difference inthe temperature of the first evaporation between every two adjacentevaporators is 5° C.-30° C.; more preferably, difference in thetemperature of the first evaporation between every two adjacentevaporators in the first evaporation is 10° C.-20° C.

In the present invention, the operating pressure of the firstevaporation preferably is the saturated vapor pressure of the evaporatedfeed liquid in the first evaporation. In addition, the amount ofevaporation in the first evaporation may be selected appropriatelyaccording to the processing capacity of the apparatus and the amount ofthe waste water to be treated. For example, the amount of evaporationmay be 0.1 m³/h or more (e.g., 0.1 m³/h-500 m³/h).

To ensure sodium chloride crystal precipitates as far as possible in thefirst evaporation process while sodium sulfate doesn't precipitate orprecipitates in a very small amount and can be dissolved in the coolingtreatment, preferably, in relation to 1 mol SO₄ ²⁻ contained in theliquid phase obtained in the first solid-liquid separation, the Cl⁻contained in the liquid phase obtained in the first solid-liquidseparation is 7.15 mol or more, preferably is 10 mol or more, morepreferably is 20 mol or more, even more preferably is 44 mol or more,further preferably is 50 mol or more, still further preferably is 74 molor more, preferably is 460 mol or less, more preferably is 230 mol orless, further preferably is 100 mol or less. For example, in relation to1 mol SO₄ ²⁻ contained in the liquid phase obtained in the firstsolid-liquid separation, the Cl⁻ contained in the liquid phase obtainedin the first solid-liquid separation may be 9.5 mol, 10.5 mol, 11 mol,11.5 mol, 12 mol, 12.5 mol, 13 mol, 13.5 mol, 14 mol, 14.5 mol, 15 mol,15.5 mol, 16 mol, 16.5 mol, 17 mol, 17.5 mol, 18 mol, 18.5 mol, 19 mol,19.5 mol, 20 mol, 21 mol, 22 mol, 23 mol, 25 mol, 27 mol, 29 mol, 31mol, 35 mol, 40 mol, 45 mol, or 50 mol, etc. By controlling the molarratio of SO₄ ²⁻ to Cl⁻ to the above-mentioned range, relatively puresodium chloride crystal can be obtained through the first evaporationand cooling treatment, separation of sodium sulfate and sodium chloridecan be realized, and energy consumption in the cooling crystallizationprocess can be reduced.

According to a preferred embodiment of the present invention, the firstevaporation ensures that the sodium sulfate in the waste water to betreated doesn't crystallize and precipitate (i.e., the sodium sulfate isnot over-saturated); preferably, through the first evaporation, theconcentration of sodium sulfate in the first concentrated solution is Yor lower, more preferably is 0.9Y-0.99Y, further preferably is0.95Y-0.98Y (wherein Y is the concentration of sodium sulfate in thefirst concentrated solution when both sodium sulfate and sodium chlorideare saturated under the conditions of the first evaporation). Bycontrolling the degree of the first evaporation within theabove-mentioned range, sodium chloride crystallizes and precipitates asfar as possible while sodium sulfate doesn't precipitate. By increasingthe amount of evaporation as far as possible, the efficiency of thewaste water treatment can be improved, and energy waste can be reduced.

According to another preferred embodiment of the present invention, toreduce the quantity of circulating water in the treatment system,improve the efficiency of the first evaporation and thereby improve theefficiency of the waste water treatment, the first evaporationpreferably is executed to a degree that both the sodium chloride and thesodium sulfate precipitate at the same time, which is to say, preferablyfirst concentrated solution that contains sodium chloride crystal andsodium sulfate crystal is obtained in the first evaporation. In thatcase, in order to obtain high-purity sodium chloride crystal, before thesecond solid-liquid separation is executed, the first concentratedsolution that contains sodium chloride crystal is treated by coolingtreatment to obtain treated solution that contains sodium chloridecrystal; then the treated solution that contains sodium chloride crystalis treated by the second solid-liquid separation. Here, the methodprovided in the present invention comprises the following steps:

1) treating waste water to be treated by cooling crystallization toobtain crystalline solution that contains sodium sulfate crystal,wherein the waste water to be treated contains the waste watercontaining ammonium salts;2) treating the crystalline solution that contains sodium sulfatecrystal by first solid-liquid separation, and treating the liquid phaseobtained in the first solid-liquid separation by first evaporation, toobtain first ammonia-containing vapor and first concentrated solutionthat contains sodium chloride crystal;3) treating the first concentrated solution that contains sodiumchloride crystal by cooling treatment, to obtain treated solution thatcontains sodium chloride crystal;4) treating the treated solution by second solid-liquid separation.

In the embodiment described above, for the purpose of improving theefficiency of the waste water treatment, the greater the degree of thefirst evaporation is, the better the result is; however, if the degreeof the first evaporation exceeds a certain degree, treated solution thatonly contains sodium chloride crystal can't be obtained through thecooling treatment; in that case, though the crystal may be dissolved,for example, by adding water into the treated solution, the efficiencyof the waste water treatment will be degraded. Therefore, preferably thefirst evaporation is executed to a degree that both sodium chloridecrystal and sodium sulfate crystal precipitate at the same time, and thesodium sulfate crystal that has precipitated can be dissolved in thecooling treatment, i.e., first concentrated solution that containssodium chloride crystal and sodium sulfate crystal is obtained throughthe step 2), and the sodium sulfate crystal in the first concentratedsolution that contains sodium chloride crystal and sodium sulfatecrystal is dissolved in the cooling treatment. To ensure that the sodiumsulfate crystal in the first concentrated solution that contains sodiumchloride crystal and sodium sulfate crystal can be dissolved in thecooling treatment, for example, the degree of the first evaporation maybe controlled so that the concentration of sodium sulfate in the treatedsolution is Y′ or lower (wherein Y′ is the concentration of sodiumsulfate when both sodium sulfate and sodium chloride are saturated inthe treated solution under the conditions of the cooling treatment), andthereby sodium chloride precipitates as far as possible while sodiumsulfate is dissolved fully in the follow-up cooling treatment procedure;preferably, after the first evaporation, the concentration of sodiumsulfate in the treated solution is 0.9Y′-0.99Y′, more preferably is0.95Y′-0.98Y′. By controlling the degree of the first evaporation to theabove-mentioned range, the sodium chloride can precipitate as far aspossible in the first evaporation process, and the sodium sulfatecrystal is dissolved fully in the cooling treatment, so that pure sodiumchloride crystal is obtained through separation finally. By causing thesodium chloride to crystallize in the first evaporation as far aspossible, the efficiency of the waste water treatment can be improved,and energy waste can be reduced.

In the present invention, the purpose of the cooling treatment is todrive the sodium sulfate crystal that is contained possibly in the firstconcentrated solution that contains sodium chloride crystal to dissolveand drive the sodium chloride to further precipitate. Causing the sodiumsulfate crystal in the first concentrated solution that contains sodiumchloride crystal to dissolve in the cooling treatment process means thatthe degree of the first evaporation must be controlled appropriately toobtain pure sodium chloride crystal, which is to say, the concentrationof sodium sulfate in the mixture system is controlled so that it doesn'texceed the corresponding solubility of sodium sulfate under theconditions of the cooling treatment. Besides, in the cooling treatmentprocess, sodium sulfate crystal may be entrained in the sodium chloridecrystal or absorbed to the surface of the sodium chloride crystal. Inthe present invention, the content of sodium sulfate in the obtainedsodium chloride crystal preferably is 8 mass % or lower, more preferablyis 4 mass % or lower. In the present invention, if the content of sodiumsulfate crystal in the obtained sodium chloride crystal is 8 mass % orlower, it is deemed that the sodium sulfate is dissolved. It should beunderstood that the quantity of the obtained sodium chloride crystal ismeasured by dry mass.

There is no particular restriction on the conditions of the coolingtreatment, as long as the above-mentioned purpose can be attainedthrough the cooling treatment. For example, the conditions of thecooling treatment may include: temperature: 13° C.-100° C., preferably15° C.-45° C., more preferably 15° C.-35° C., further preferably 17.9°C.-35° C.; still further preferably 17.9° C.-25° C. To ensure the effectof the cooling treatment, preferably, the conditions of the coolingtreatment include: time: 5 min. or longer, preferably 5 min.-120 min.,more preferably 30 min.-90 min.; further preferably 50 min.-60 min.Examples of the temperature of the cooling treatment may include: 13°C., 14° C., 15° C., 15.5° C., 16° C., 16.5° C., 17° C., 17.5° C., 17.9°C., 18° C., 18.5° C., 19° C., 19.5° C., 20° C., 21° C., 23° C., 25° C.,27° C., 30° C., 31° C., 31.5° C., 32° C., 33° C., 34° C., 35° C., 40°C., 45° C., 50° C., or 55° C., etc.

Examples of the time of the cooling treatment may include: 5 min., 6min., 7 min., 8 min., 10 min., 15 min., 20 min., 25 min., 30 min., 35min., 40 min., 45 min., 50 min., 52 min., 54 min., 56 min., 58 min., 60min., 70 min., 100 min., or 120 min.

According to the present invention, the cooling treatment is executed ina low temperature treatment tank 55. After the first concentratedsolution that contains sodium chloride crystal is treated by coolingtreatment in the low temperature treatment tank 55, the treated solutionthat contains sodium chloride crystal is obtained. There is noparticular restriction on the low temperature treatment tank 55. Forexample, the low temperature treatment tank 55 may be a thickener, acrystallization tank with a stirrer, or a crystallization tank withexternal circulation, wherein preferably the low temperature treatmenttank 55 is a crystallization tank with a stirrer. Preferably the lowtemperature treatment tank 55 is equipped with a mixing component, whichmixes the first concentrated solution to a homogeneous state in thecooling treatment process. For example, the low temperature treatmenttank 55 may be equipped with a conventional mechanical stirrer,electromagnetic stirrer, and/or external circulation device, whichpreferably maintains the solid-liquid distribution in the firstconcentrated solution in a homogeneous state. By mixing the firstconcentrated solution to a homogenous state, the parts of the firstconcentrated solution are maintained in a uniform temperature andconcentration state, so as to avoid insufficient dissolution of sodiumsulfate crystal and improve the efficiency of the cooling treatment.Preferably the low temperature treatment tank 55 has a coolingcomponent, which decreases the temperature in the low temperaturetreatment tank 55 to a value required for the cooling treatment byintroducing a cooling medium.

In the present invention, the degree of the first evaporation isascertained by monitoring the amount of evaporation (or amount of thecondensate) in the first evaporation or the concentration of the firstconcentrated solution. Specifically, if the degree of the firstevaporation is ascertained by measuring the amount of evaporation,concentration ratio is controlled by controlling the amount ofevaporation (i.e., the amount of secondary steam or amount of firstammonia water), and the degree of the concentration by first evaporationis monitored by measuring the amount of evaporation, so that the sodiumsulfate crystal precipitating in the first concentrated solutionobtained in the first evaporation can be dissolved in the coolingtreatment. Specifically, a mass flow meter may be used to measure theflow and thereby measure the amount of the secondary steam, or theamount of the condensate may be measured; if the degree of the firstevaporation is ascertained by measuring the concentration, the sodiumsulfate in the first concentrated solution doesn't crystallize andprecipitate in the first evaporation by controlling the concentration ofthe first concentrated solution obtained in the first evaporation withinthe above-mentioned range, and the concentration of the liquid obtainedin the first evaporation is monitored by measuring the density;specifically, a densitometer may be used to measure the density.

According to the present invention, to take full advantage of the heatin the first ammonia-containing vapor obtained in the first evaporation,preferably second heat exchange between the first mother liquid and thefirst ammonia-containing vapor is executed, before the first motherliquid is fed into the first MVR evaporation device 1.

According to a preferred embodiment of the present invention, the secondheat exchange between the first mother liquid and the firstammonia-containing vapor is executed in a third heat exchange device 33and a fourth heat exchange device 34 respectively. Specifically, thefirst mother liquid flows through the third heat exchange device 33 andthe fourth heat exchange device 34 sequentially, and the firstammonia-containing vapor flows through the fourth heat exchange device34 and the third heat exchange device 33 sequentially, so that thetemperature of the first mother liquid is increased to facilitate thefirst evaporation, while the first ammonia-containing vapor is condensedto obtain first ammonia water. After the heat exchange in the third heatexchange device 33, the temperature of the first mother liquid isincreased to 44° C.-174° C., preferably 94° C.-109° C.; after the heatexchange in the fourth heat exchange device 34, the temperature of thefirst mother liquid is increased to 52° C.-182° C., preferably 102°C.-117° C.

According to the present invention, to take full advantage of the heatin the first crystal-containing concentrated solution obtained in thefirst evaporation, preferably second heat exchange between the firstcrystal-containing concentrated solution and the first mother liquid isexecuted before the cooling treatment.

According to a preferred embodiment of the present invention, the secondheat exchange between the first crystal-containing concentrated solutionand the first mother liquid is executed in a fifth heat exchange device35. Specifically, the first mother liquid and the firstcrystal-containing concentrated solution flow through the fifth heatexchange device 35 respectively, so that the temperature of the firstmother liquid is increased to facilitate first evaporation, while thefirst crystal-containing concentrated solution is cooled to facilitatecooling treatment. After the heat exchange in the fifth heat exchangedevice 35, the temperature of the first mother liquid is increased to44° C.-174° C., preferably 94° C.-109° C.

According to the present invention, preferably the pH value of the firstmother liquid is adjusted to a value greater than 9, preferably greaterthan 10.8, before the first mother liquid (i.e., the liquid phaseobtained in the first solid-liquid separation) is fed into the first MVRevaporation device 1. Besides, there is no particular restriction on theupper limit of adjustment of the pH value of the first mother liquid.For example, the adjusted pH value may be 14 or lower, preferably is13.5 or lower, more preferably is 13 or lower, further preferably is 12or lower, still further preferably is 11.5 or lower. By adjusting the pHof the first mother liquid to the above-mentioned range, ammonia can befully evaporated in the first evaporation process, and thereby thepurity of the obtained sodium chloride can be improved. The pHadjustment for the first mother liquid may be executed with reference tothe pH adjustment for the waste water to be treated as described above,except that the target range of the pH adjustment is different.

For example, before the first mother liquid is fed into the first MVRevaporation device 1, the pH value of the first mother liquid may beadjusted to any of the following values: 9, 9.5, 9.6, 9.7, 9.8, 9.9, 10,10.1, 10.2, 10.3, 10.4, 10.5, 10.6, 10.7, 10.8, 10.9, 11, 11.1, 11.2,11.3, 11.4, 11.5, 11.6, 11.7, 11.8, 11.9, 12, 12.2, 12.4, 12.6, 12.8,13, 13.5, or 14, etc.

According to a preferred embodiment of the present invention, before thefirst mother liquid is fed into the first MVR evaporation device 1,water solution of an alkaline substance is introduced into the pipelinethrough which the first mother liquid is fed into the first MVRevaporation device 1, and is mixed with the first mother liquid, toattain the purpose of pH adjustment. In addition, the pH value of thefirst mother liquid after the adjustment may be monitored with a secondpH measuring device 62.

According to the present invention, the second solid-liquid separationmay be executed in a second solid-liquid separation device 92 (e.g.,centrifugal machine, band filter, or plate and frame filter, etc.).After the second solid-liquid separation, the second mother liquidobtained in the second solid-liquid separation device 92 (i.e., theliquid phase obtained in the second solid-liquid separation) is returnedto the cooling crystallization device 2 for further coolingcrystallization, or is returned to the concentration device forconcentration. Specifically, the second mother liquid may be returned bymeans of a ninth circulation pump 79 to a position just before the firstpH adjustment. Besides, it is inevitable that the obtained sodiumchloride crystal has some impurities absorbed thereon, such as sulfateions, free ammonia, and hydroxyl ions, etc. Preferably, the sodiumchloride crystal is washed in a second washing with water, the wastewater containing ammonium salts, or sodium chloride solution and dried,to remove the absorbed impurities, reduce off-odor of the solid salt,decrease causticity, and improve the purity of the crystal. To preventthe sodium chloride crystal from dissolved in the washing process,preferably, the sodium chloride crystal is washed with sodium chloridesolution. More preferably, the concentration of the sodium chloridesolution preferably is the concentration of sodium chloride in watersolution where sodium chloride and sodium sulfate are saturated at thesame time at the temperature corresponding to the sodium chloridecrystal to be washed. The second washing preferably is elutriationfollowed by elution. The second washing liquid obtained in the abovewashing process preferably is returned by means of a tenth circulationpump 80 to the first MVR evaporation device 1 for first evaporationagain.

There is no particular restriction on the specific method for the secondsolid-liquid separation and the second washing. For example, the secondsolid-liquid separation and the second washing may be executed withconventional elutriation apparatus and solid-liquid separation apparatusin combination, or may be executed in a staged solid-liquid separationapparatus, such as a band filter. There is no particular restriction onthe elutriation and elution. In other words, they can be executed with aconventional method in the art. There is no particular restriction onthe number of cycles of the elutriation and elution. For example, onecycle or more may be selected. To obtain sodium chloride crystal athigher purity, preferably the elutriation and elution are executed for2-4 cycles. In the elutriation process, the elutriating liquid usuallyis not reused by circulation if the waste water containing ammoniumsalts is used as the elutriating liquid; or the elutriating liquid maybe reused by counter-current circulation if the washing liquid recycledin the second washing is used as the elutriating liquid. Before theelutriation is executed, preferably slurry that contains sodium chloridecrystal (as long as the liquid content is 35 mass % or lower) isobtained through preliminary solid-liquid separation by sedimentation.In the elutriation process, in relation to 1 pbw slurry that containssodium chloride crystal, the liquid used for the elutriation is 1-20pbw. The elution preferably is executed with sodium chloride solution(the concentration of the sodium chloride solution preferably is theconcentration of sodium chloride in water solution where both sodiumchloride and sodium sulfate are saturated at the temperaturecorresponding to the sodium chloride crystal to be washed). To furtherimprove the effect of the elutriation and obtain sodium chloride crystalat higher purity, the elutriation is executed preferably with the eluentobtained in the elution. For the liquid produced in the washing,preferably the washing liquid (water or sodium chloride solution) andthe elutriant are returned to the first MVR evaporation device 1.

According to a preferred embodiment of the present invention, the firstconcentrated solution that contains sodium chloride crystal or thetreated solution that contains sodium chloride crystal is elutriated inanother elutriation tank with the liquid obtained in the follow-upsodium chloride crystal washing after it is treated by preliminarysolid-liquid separation by means of sedimentation, and then theelutriated treated solution that contains sodium chloride crystal is fedinto a solid-liquid separation device for solid-liquid separation; thecrystal obtained in the solid-liquid separation is eluted with sodiumchloride solution (the concentration of the sodium chloride solutionpreferably is the concentration of sodium chloride in the water solutionwhen both sodium chloride and sodium sulfate are saturated at thetemperature corresponding to the sodium chloride crystal to be washed),and the liquid obtained in the elution is returned as elutriant to theelutriation process. Through the above washing process that incorporateselutriation and elution, the purity of the obtained sodium chloridecrystal is improved, no excessive washing liquid is introduced into thesystem, and the efficiency of the waste water treatment is improved.

In a fifth aspect, the present invention provides a method for treatingwaste water containing ammonium salts that contains NH₄ ⁺, SO₄ ²⁻, Cl⁻and Na⁺ as shown in FIGS. 6-7, which comprises the following steps:

1) treating waste water to be treated by second evaporation, to obtainsecond ammonia-containing vapor and second concentrated solution thatcontains sodium sulfate crystal, wherein the waste water to be treatedcontains the waste water containing ammonium salts;2) treating the second concentrated solution that contains sodiumsulfate crystal by third solid-liquid separation, and treating theliquid phase obtained in the third solid-liquid separation by coolingcrystallization, to obtain crystalline solution that contains sodiumsulfate crystal;3) treating the crystalline solution that contains sodium sulfatecrystal by fourth solid-liquid separation, and treating the liquid phaseobtained in the fourth solid-liquid separation by third evaporation, toobtain third ammonia-containing vapor and third concentrated solutionthat contains sodium chloride crystal;4) treating the third concentrated solution that contains sodiumchloride crystal by fifth solid-liquid separation;wherein the pH of the waste water to be treated is adjusted to a valuegreater than 9, before the waste water to be treated is treated by thesecond evaporation; in relation to 1 mol SO₄ ²⁻ contained in the wastewater to be treated, the Cl⁻ contained in the waste water to be treatedis 14 mol or less; the second evaporation is executed in a way that nosodium chloride crystallizes and precipitates.

Preferably, the waste water to be treated is the waste water containingammonium salts; or the waste water to be treated contains the wastewater containing ammonium salts and the liquid phase obtained in thefifth solid-liquid separation.

More preferably, the waste water to be treated is mixed solution of thewaste water containing ammonium salts and at least a part of the liquidphase obtained in the fifth solid-liquid separation.

The method provided in the present invention can treat waste watercontaining ammonium salts, which contains NH₄ ⁺, SO₄ ²⁻, Cl⁻ and Na⁺,and there is no particular restriction on the waste water containingammonium salts, except that the waste water contains NH₄ ⁺, SO₄ ²⁻, Cl⁻and Na⁺.

In the present invention, there is no particular restriction on theorder of the first heat exchange, the adjustment of pH value of thewaste water to be treated, and the blending process of the waste waterto be treated (in the case that the waste water to be treated containsthe waste water containing ammonium salts and the liquid phase obtainedin the fifth solid-liquid separation, a blending process of the wastewater to be treated is required), and the order may be selectedappropriately as required, as long as those procedures are accomplishedbefore the second evaporation of the waste water to be treated.

In the present invention, the purpose of the second evaporation is toderive the sodium sulfate to crystallize and precipitate, concentratethe waste water to be treated, and obtain relatively thick ammonia waterat the same time, so as to improve ion concentration and precipitationratio of cooling crystallization. The degree of the second evaporationmay be selected as required according to the components of the wastewater to be treated, as long as only sodium sulfate crystallizes andprecipitates. For example, the evaporation may be controlled so thatonly a small quantity of ammonia-containing vapor is obtained, andthereby ammonia water at relatively high concentration is obtained;alternatively, the degree of the evaporation may be controlled so thatthe waste water to be treated is concentrated, and the ion concentrationis controlled at the same time so that pure sodium sulfate can beobtained in the follow-up cooling crystallization; or the evaporationmay be controlled to complete fully, so that the waste water to betreated is concentrated and the efficiency of cooling crystallizationcan be improved.

In the present invention, the device used for the second evaporation isthe same as that used for the first evaporation, and will not be furtherdetailed here. For example, the second evaporation may be executed in asecond MVR evaporation device 3.

According to the present invention, there is no particular restrictionon the conditions of the second evaporation, as long as the purpose ofconcentrating the waste water to be treated is attained. For example,the conditions of the second evaporation may include: temperature: 35°C. or above; pressure: −98 kPa or above. To improve the efficiency ofevaporation, preferably, the conditions of the second evaporationinclude: temperature: 75° C.-130° C.; pressure: −73 kPa-117 kPa;preferably, the conditions of the second evaporation include:temperature: 85° C.-130° C.; pressure: −58 kPa-117 kPa; preferably, theconditions of the second evaporation include: temperature: 95° C.-110°C.; pressure: −37 kPa-12 kPa; preferably, the conditions of the secondevaporation include: temperature: 95° C.-105° C.; pressure: −37 kPa-−7kPa.

In the present invention, the operating pressure of the secondevaporation preferably is the saturated vapor pressure of the evaporatedfeed liquid. In addition, the amount of evaporation in the secondevaporation may be selected appropriately according to the processingcapacity of the apparatus and the amount of the waste water to betreated. For example, the amount of evaporation may be 0.1 m³/h or more(e.g., 0.1 m³/h-500 m³/h).

For the purpose of improving the waste water treatment efficiency, inrelation to 1 mol SO₄ ²⁻ contained in the waste water to be treated, theCl⁻ contained in the waste water to be treated is 14 mol or less,preferably is 13.8 mol or less, more preferably is 13.75 mol or less,even more preferably is 13.5 mol or less, further preferably is 13 molor less, still further preferably is 12 mol or less, still furtherpreferably is 11 mol or less, still further preferably is 10.5 mol orless, preferably is 2 mol or more, more preferably is 2.5 mol or more,further preferably is 3 mol or more, e.g., 1.5-6.02 mol. By controllingthe molar ratio of SO₄ ²⁻ to Cl⁻ to the above-mentioned range, sodiumsulfate precipitates while sodium chloride doesn't precipitate in thesecond evaporation.

By controlling the conditions of the second evaporation appropriately,the ammonia contained in the waste water to be treated obtained in theevaporation may be 80 mass % or higher, preferably is 90 mass % orhigher, e.g., 80 mass %, 83 mass %, 85 mass %, 86 mass %, 87 mass %, 88mass %, 89 mass %, 90 mass %, 91 mass %, 93 mass %, 95 mass %, or 98mass %, etc. The first ammonia water may be directly reused in acatalyst production process, or may be neutralized with acid to obtainammonium salts and then the ammonium salts are reused, or may be blendedwith water and corresponding ammonium salts or ammonia water and thenreused.

According to a preferred embodiment of the present invention, throughthe second evaporation, the concentration of sodium chloride in thesecond concentrated solution is X or lower, where, X is theconcentration of sodium chloride in the second concentrated solutionwhen both sodium chloride and sodium sulfate are saturated under theconditions of the second evaporation. Preferably, through the secondevaporation, the concentration of sodium chloride in the secondconcentrated solution is 0.95X-0.999X. If sodium sulfate crystal is onlyobtained in the cooling crystallization, preferably, the concentrationof Cl⁻ in the liquid phase obtained in the third solid-liquid separation(i.e., third mother liquid) is 5.2 mol/L or lower; more preferably, theconcentration of Cl⁻ in the liquid phase obtained in the thirdsolid-liquid separation is 5.0 mol/L or lower. By controlling the degreeof the second evaporation, sodium sulfate crystallizes and precipitatesas far as possible, and the concentration of chloride ions in the liquidphase obtained in the third solid-liquid separation meets the criterionfor preventing sodium chloride from precipitating in the coolingcrystallization at the same time, and thereby the efficiency of thewaste water treatment can be improved.

In the present invention, the degree of the second evaporation isascertained by monitoring the concentration of the liquid obtained inthe second evaporation. Specifically, by controlling the concentrationof the liquid obtained in the second evaporation within theabove-mentioned range, the sodium chloride doesn't crystallize andprecipitate in the second evaporation. Here, the concentration of theliquid obtained in the second evaporation is monitored by measuring thedensity of the liquid; specifically, the density may be measured with adensitometer.

According to the present invention, the pH value of the waste water tobe treated is adjusted to a value greater than 9, preferably greaterthan 10.8, before the waste water to be treated is treated by the secondevaporation. Besides, there is no particular restriction on the upperlimit of pH adjustment of the waste water to be treated. For example,the pH may be 14 or lower, preferably is 13.5 or lower, more preferablyis 13 or lower. By executing the second evaporation at theabove-mentioned pH value, ammonia evaporation can be promoted, ammoniawater at relatively high concentration can be obtained, and high-puritysodium sulfate and sodium chloride crystal can be obtained in thefollow-up crystallization process.

For example, before the waste water to be treated is treated by thesecond evaporation, the pH value of the waste water to be treated may beadjusted to any of the following values: 9, 9.5, 9.6, 9.7, 9.8, 9.9, 10,10.1, 10.2, 10.3, 10.4, 10.5, 10.6, 10.7, 10.8, 10.9, 11, 11.1, 11.2,11.3, 11.4, 11.5, 11.6, 11.7, 11.8, 11.9, 12, 12.2, 12.4, 12.6, 12.8,13, 13.5, or 14, etc.

In the present invention, there is no particular restriction on the pHadjustment method. For example, the pH value of the waste water to betreated may be adjusted by adding an alkaline substance. There is noparticular restriction on the alkaline substance, as long as thealkaline substance can attain the purpose of adjusting the pH. To avoidintroducing any new impurity into the waste water to be treated andimprove the purity of the obtained crystal, the alkaline substancepreferably is NaOH. In addition, in view that the fifth mother liquid(i.e., the liquid phase obtained in the fifth solid-liquid separation)contains NaOH at relatively high concentration, preferably the fifthmother liquid is used as the alkaline substance, and additional NaOH maybe added.

The alkaline substance may be added with a conventional method in theart. However, preferably the alkaline substance is mixed in the form ofwater solution with the waste water to be treated. For example, watersolution that contains the alkaline substance may be charged into apipeline through which the waste water to be treated is inputted. Thereis no particular restriction on the content of the alkaline substance inthe water solution, as long as the water solution can attain the purposeof adjusting the pH. However, to reduce the amount of water and furtherreduce the cost, preferably saturated water solution of the alkalinesubstance or the fifth mother liquid is used. To monitor the pH of thewaste water to be treated, the pH of the waste water to be treated maybe measured after the pH adjustment.

According to a preferred embodiment of the present invention, the secondevaporation is executed in a second MVR evaporation device 3. Before thewaste water to be treated is fed into the second MVR evaporation device3, the pH value is adjusted by introducing the water solution thatcontains an alkaline substance into the pipeline through which the wastewater to be treated is fed into the second MVR evaporation device 3 andmixing the water solution that contains an alkaline substance with thewaste water to be treated there, and the adjusted pH value is measuredwith a first pH measuring device 61 and a second pH measuring device 60.

According to the present invention, to take full advantage of the heatin the second ammonia-containing vapor, preferably first heat exchangebetween the waste water to be treated and the second ammonia-containingvapor is executed before the waste water to be treated is treated bysecond evaporation, to obtain first ammonia water and increase thetemperature of the waste water to be treated at the same time tofacilitate evaporation.

According to a preferred embodiment of the present invention, the firstheat exchange between the waste water to be treated and the secondammonia-containing vapor is executed in a first heat exchange device 31and an eighth heat exchange device 38. Specifically, theammonia-containing vapor flows through the eighth heat exchange device38 and the first heat exchange device 31 sequentially, and the wastewater to be treated flows through the first heat exchange device 31 toexchange heat with condensate of the second ammonia-containing vapor,and then flows through the eighth heat exchange device 38 to exchangeheat with the second ammonia-containing vapor. Through the first heatexchange, first ammonia water is obtained and stored in a first ammoniawater storage tank 51, and the temperature of the waste water to betreated is increased to 82° C.-137° C. at the same time, preferably isincreased to 102° C.-117° C., to facilitate evaporation.

According to the present invention, to take full advantage of the heatin the second concentrated solution, preferably first heat exchangebetween the waste water to be treated and the second concentratedsolution is executed before the waste water to be treated is treated bysecond evaporation, so that the temperature of the second concentratedsolution is decreased to facilitate cooling crystallization, while thetemperature of the waste water to be treated is increased to facilitateevaporation.

According to a preferred embodiment of the present invention, the firstheat exchange between the waste water to be treated and the secondconcentrated solution is executed in an eleventh heat exchange device30; thus, the waste water to be treated exchanges heat with the secondconcentrated solution in the eleventh heat exchange device 30.

In the present invention, through third solid-liquid separation of thesecond concentrated solution that contains sodium sulfate crystal,sodium sulfate crystal and third mother liquid (i.e., the liquid phaseobtained in the third solid-liquid separation) are obtained. There is noparticular restriction on the method of the third solid-liquidseparation. For example, the method may be selected from one or more ofcentrifugation, filtering, and sedimentation.

According to the present invention, the third solid-liquid separationfor the second concentrated solution may be executed in a thirdsolid-liquid separation device 93 (e.g., centrifugal machine, bandfilter, or plate and frame filter, etc.). As shown in FIG. 6, after thethird solid-liquid separation, the third mother liquid obtained in thethird solid-liquid separation device 93 is stored temporarily in a thirdmother liquid tank 50, and may be fed by means of an eleventhcirculation pump 70 into the cooling crystallization device 2 forcooling crystallization. In addition, preferably the solid phaseobtained in the third solid-liquid separation is washed by thirdwashing.

The third solid-liquid separation and the third washing may be executedin the same way as the first solid-liquid separation and the firstwashing respectively, and will not be further detailed here. The liquidproduced in the washing preferably is returned to a position before thefirst heat exchange is completed before the second evaporation.

According to a preferred embodiment of the present invention, after thesecond concentrated solution that contains sodium sulfate crystal istreated through preliminary solid-liquid separation by sedimentation,the obtained solution is elutriated for the first time with the wastewater containing ammonium salts in an elutriation tank, then iselutriated for the second time with the liquid obtained in the follow-upsodium sulfate crystal washing in another elutriation tank, and finallythe slurry obtained through twice elutriations is fed into the secondsolid-liquid separation device for solid-liquid separation; then, thecrystal obtained in the solid-liquid separation is eluted with sodiumsulfate solution, and the liquid obtained in the elution is returned tothe second elutriation. Through the above washing process, the purity ofthe obtained sodium sulfate crystal is improved, no excessive washingliquid is introduced into the system, and the efficiency of the wastewater treatment is improved.

In the present invention, crystalline solution that only contains sodiumsulfate crystal or crystalline solution that contains sodium sulfatecrystal and sodium chloride crystal may be obtained in the coolingcrystallization. If the cooling crystallization is executed for apurpose of driving the sodium sulfate to precipitate so that the sodiumsulfate is separated from the waste water, preferably the coolingcrystallization is executed in a way that ensures the crystallinesolution obtained in the cooling crystallization only contains sodiumsulfate crystal. Here, the obtained sodium sulfate crystal (i.e., thesolid phase obtained in the fourth solid-liquid separation) is sodiumsulfate hydrate crystal (e.g., sodium sulfate decahydrate crystal),which may be directly used as a product; or the combined water in thesodium sulfate hydrate crystal may be removed, e.g., through a heatingprocedure, to obtain sodium sulfate crystal; or the sodium sulfatehydrate crystal may be returned to the second evaporation process forevaporation so as to obtain sodium sulfate crystal that doesn't includecombined water. In addition, if the cooling crystallization is executedfor a purpose of obtaining sodium sulfate that doesn't include combinedwater, the cooling crystallization may be executed in a way that ensuresthe obtained crystalline solution contains sodium sulfate crystal(sodium sulfate crystal hydrate) and sodium chloride crystal. Here,preferably the sodium sulfate crystal and sodium chloride crystalobtained in the cooling crystallization (i.e., the solid phase obtainedin the fourth solid-liquid separation) are returned to the secondevaporation process together for evaporation, so as to obtain sodiumsulfate crystal that doesn't include combined water. As a method forreturning the crystal obtained in the cooling crystallization to thesecond evaporation process, preferably it is returned to a positionbefore the pH adjustment and the first heat exchange procedures beforethe second evaporation; for example, the crystal may be returned to thewaste water pipeline before the first pH adjustment device 61.

According to a preferred embodiment of the present invention, to obtainhigh-purity sodium sulfate crystal, preferably the coolingcrystallization is executed in a way that no sodium chloride crystalprecipitates, i.e., crystalline solution that only contains sodiumsulfate crystal is obtained, so that the sodium sulfate can be separatedfrom the waste water successfully. The cooling crystallization onlydrives the sodium sulfate to precipitate, but doesn't exclude sodiumchloride, which is entrained in the sodium sulfate crystal or absorbedto the surface of the sodium sulfate crystal. In the present invention,preferably the content of sodium sulfate in the obtained sodium sulfatecrystal is 92 mass % or higher, more preferably is 96 mass % or higher,further preferably is 98 mass % or higher. It should be understood thatthe quantity of the obtained sodium sulfate crystal is measured by drymass. If the content of sodium sulfate in the obtained sodium sulfatecrystal is within the above-mentioned range, it is deemed that onlysodium sulfate precipitates. Namely, if the total content of impurities(sodium chloride, etc.) in the obtained sodium sulfate crystal is 8 mass% or lower, it is deemed that only sodium sulfate precipitates.

To ensure that sodium sulfate crystal is obtained in the coolingcrystallization, the concentration of SO₄ ²⁻ in the third mother liquidpreferably is 0.01 mol/L or higher, more preferably is 0.07 mol/L orhigher, further preferably is 0.1 mol/L or higher, still furtherpreferably is 0.2 mol/L or higher, particularly preferably is 0.3 mol/Lor higher. According to the present invention, to improve the purity ofthe sodium sulfate crystal obtained in the cooling crystallization, theconcentration of Cl⁻ in the third mother liquid preferably is 5.2 mol/Lor lower, more preferably is 5 mol/L or lower, further preferably is 4.5mol/L or lower, still further preferably is 4 mol/L or lower, so thatthe sodium chloride doesn't precipitate in the cooling crystallization.

By controlling the concentration values of SO₄ ²⁻ and Cl⁻ in the thirdmother liquid within the above-mentioned ranges, the second evaporationcan be executed fully, and sodium sulfate crystalizes and precipitatesbut sodium chloride doesn't precipitate in the cooling crystallization,and thereby a purpose of separating sodium sulfate efficiently isattained. In the present invention, if the concentration of SO₄ ²⁻ orCl⁻ in the third mother liquid is not within the above-mentioned range,the concentration may be adjusted before the cooling crystallization isexecuted. Preferably, the concentration may be adjusted with the wastewater containing ammonium salts, the sodium sulfate crystal washingliquid, and/or the fifth mother liquid, etc., which may be mixed withthe fifth mother liquid in the third mother liquid tank 50 specifically.

Examples of the content of SO₄ ²⁻ in the third mother liquid mayinclude: 0.01 mol/L, 0.03 mol/L, 0.05 mol/L, 0.08 mol/L, 0.1 mol/L, 0.2mol/L, 0.3 mol/L, 0.4 mol/L, 0.5 mol/L, 0.6 mol/L, or 0.7 mol/L, etc.

In addition, examples of the content of Cl⁻ in the third mother liquidmay include: 2.0 mol/L, 2.2 mol/L, 2.4 mol/L, 2.6 mol/L, 2.8 mol/L, 3mol/L, 3.2 mol/L, 3.4 mol/L, 3.6 mol/L, 3.8 mol/L, 4 mol/L, 4.5 mol/L,or 5 mol/L, etc.

According to another preferred embodiment of the present invention, ifthe solid phase obtained in the fourth solid-liquid separation is notused as a product of the waste water treatment, the coolingcrystallization may be executed in a way that sodium chloridecrystallizes and precipitates, i.e., sodium sulfate crystal and sodiumchloride crystal are obtained at the same time in the coolingcrystallization; here, the sodium sulfate crystal and sodium chloridecrystal obtained in the cooling crystallization are returned to thesecond evaporation process together for evaporation, so as to obtainsodium sulfate crystal that doesn't include combined water. By using thesecond evaporation and the cooling crystallization in combination, thesecond evaporation is easier to control, and the efficiency of wastewater treatment is improved as well.

By adjusting the pH value of the waste water to be treated to a valuegreater than 9 before the second evaporation, the majority of NH₄ ⁺ isevaporated out in the form of ammonia molecules in the secondevaporation; thus, ammonium sulfate and/or ammonium chloride will notprecipitate in the cooling crystallization process, and theprecipitation ratio of sodium sulfate can be improved because theconcentration of sodium chloride is improved.

According to the present invention, the conditions of the coolingcrystallization are the same as the conditions of the coolingcrystallization in the method in the third aspect, and will not befurther detailed here.

In the present invention, through fourth solid-liquid separation of thecrystalline solution that contains sodium sulfate crystal, sodiumsulfate crystal and fourth mother liquid (i.e., the liquid phaseobtained in the fourth solid-liquid separation) are obtained. There isno particular restriction on the method of the fourth solid-liquidseparation. For example, the method may be selected from one or more ofcentrifugation, filtering, and sedimentation.

According to the present invention, the fourth solid-liquid separationmay be performed in a first solid-liquid separation device 91 (e.g.,centrifugal machine, band filter, or plate and frame filter, etc.).After the fourth solid-liquid separation, the fourth mother liquidobtained in the first solid-liquid separation device 91 is storedtemporarily in a first mother liquid tank 53, and may be pumped by asixth circulation pump 76 into the first MVR evaporation device 1 forthird evaporation. In addition, preferably the solid phase obtained inthe fourth solid-liquid separation is washed by fourth washing.

The fourth solid-liquid separation and the fourth washing may beexecuted in the same way as the first solid-liquid separation and thefirst washing respectively, and will not be further detailed here. Forthe liquid produced in the washing, preferably the washing liquid (wateror sodium sulfate solution) is returned to the cooling crystallizationdevice 2. For example, the liquid may be returned by means of an eighthcirculation pump 78 to the cooling crystallization device 2.

According to a preferred embodiment of the present invention, after thecrystalline solution that contains sodium sulfate is obtained throughcooling crystallization, solid-liquid separation is executed with asolid-liquid separation device, and the crystal obtained in thesolid-liquid separation is eluted with sodium sulfate solution (theconcentration of the sodium sulfate solution is the concentration ofsodium sulfate in water solution where both sodium chloride and sodiumsulfate are saturated at the temperature corresponding to the sodiumsulfate crystal to be washed), and the liquid obtained in the elution isreturned to the cooling crystallization device 2. Through the washingprocess described above, the purity of the obtained sodium sulfatecrystal can be improved.

According to the present invention, to take full advantage of thecooling capacity of the fourth mother liquid, preferably second heatexchange between the fourth mother liquid and the third mother liquid isexecuted before the third mother liquid is treated by coolingcrystallization.

According to a preferred embodiment of the present invention, the secondheat exchange is executed in a second heat exchange device 32;specifically, the fourth mother liquid and the third mother liquid flowthrough the second heat exchange device 32 respectively, so that theyexchange heat and thereby the temperature of the third mother liquid isdecreased to facilitate cooling crystallization, while the temperatureof the fourth mother liquid is increased to facilitate thirdevaporation. After the second heat exchange in the second heat exchangedevice 32, the temperature of the third mother liquid is −20.7° C.-16.5°C., preferably is −5° C.-10° C., close to the temperature of coolingcrystallization.

According to the present invention, to facilitate coolingcrystallization, second heat exchange between the third mother liquidand refrigerating liquid is executed. According to a preferredembodiment of the present invention, the second heat exchange betweenthe third mother liquid and the refrigerating liquid is executed in asixth heat exchange device 36; specifically, the refrigerating liquidand the third mother liquid flow through the sixth heat exchange device36 respectively so that they exchange heat with each other, and therebythe temperature of the third mother liquid is decreased to facilitatecooling crystallization. The refrigerating liquid may be anyconventional refrigerating liquid for cooling in the art, as long as itcan cool the third mother liquid to a temperature that meets the coolingcrystallization requirement.

In the present invention, the device used for the third evaporation isthe same as that used for the first evaporation, and will not be furtherdetailed.

According to a preferred embodiment of the present invention, in a casethat the cooling treatment is not used, the purpose of the thirdevaporation is to drive the sodium chloride to precipitate and evaporatethe ammonia further, so as to attain a purpose of separating the ammoniaand salts in the waste water.

In the present invention, there is no particular restriction on theevaporation conditions of the third evaporation; in other words, theevaporation conditions may be selected appropriately as required, aslong as the purpose of crystallization can be attained. The conditionsof the third evaporation may include: temperature: temperature: 17.5° C.or above; pressure: −101 kPa or above; preferably, the conditions of thethird evaporation include: temperature: 35° C.-110° C.; pressure: −98kPa-12 kPa; preferably, the conditions of the third evaporation include:temperature: 45° C.-110° C.; pressure: −95 kPa-12 kPa; preferably, theconditions of the third evaporation include: temperature: 50° C.-100°C.; pressure: −93 kPa-−22 kPa.

In the present invention, the operating pressure of the thirdevaporation preferably is the saturated vapor pressure of the evaporatedfeed liquid. In addition, the amount of evaporation in the thirdevaporation may be selected appropriately according to the processingcapacity of the apparatus and the amount of the waste water to betreated. For example, the amount of evaporation may be 0.1 m³/h or more(e.g., 0.1 m³/h-500 m³/h).

To obtain sodium chloride crystal in the third evaporation process in abetter way, preferably, in relation to 1 mol SO₄ ²⁻ contained in theliquid phase obtained in the fourth solid-liquid separation, the Cl⁻contained in the liquid phase obtained in the fourth solid-liquidseparation is 7.15 mol or more, preferably is 10 mol or more, preferablyis 20 mol or more, more preferably is 44 mol or more, more preferably is50 mol or more, more preferably is 74 mol or more, preferably is 460 molor less, more preferably is 230 mol or less, e.g., 43.4-49.8 mol, suchas 9.5 mol, 10.5 mol, 11 mol, 11.5 mol, 12 mol, 12.5 mol, 13 mol, 13.5mol, 14 mol, 14.5 mol, 15 mol, 15.5 mol, 16 mol, 16.5 mol, 17 mol, 17.5mol, 18 mol, 18.5 mol, 19 mol, 19.5 mol, 20 mol, 21 mol, 22 mol, 23 mol,25 mol, 27 mol, 29 mol, 31 mol, 35 mol, 40 mol, 45 mol, 50 mol, 60 mol,or 65 mol, etc. By controlling the molar ratio of SO₄ ²⁻ to Cl⁻ to theabove-mentioned range, high-purity sodium chloride crystal can beobtained through the third evaporation, and separation of sodium sulfateand sodium chloride can be realized.

According to the present invention, for the purpose of improving theefficiency of the waste water treatment, the greater the degree of thethird evaporation is, the better the result is; however, if the degreeof the third evaporation exceeds a certain degree, third concentratedsolution that only contains sodium chloride crystal can't be obtained;in that case, though the crystal may be dissolved, for example, byadding water into the third concentrated solution, the efficiency of thewaste water treatment will be degraded. Therefore, preferably the thirdevaporation is executed to a degree that no sodium sulfate crystalcrystallizes and precipitates, which is to say, through the thirdevaporation, the concentration of sodium sulfate in the thirdconcentrated solution is Y or lower (wherein Y is the concentration ofsodium sulfate in the third concentrated solution when both sodiumsulfate and sodium chloride are saturated under the conditions of thethird evaporation). In view of driving the sodium chloride toprecipitate as far as possible while preventing the sodium sulfate fromprecipitating in the third evaporation procedure, preferably, throughthe third evaporation, the concentration of sodium sulfate in the thirdconcentrated solution is 0.9Y-0.99Y, more preferably is 0.95Y-0.98Y. Bycontrolling the degree of the third evaporation to the above-mentionedrange, the sodium chloride can precipitate as far as possible in thethird evaporation process, and the sodium sulfate doesn't precipitate,so that pure sodium chloride crystal is obtained through separationfinally. By causing the sodium chloride to crystallize in the thirdevaporation as far as possible, the efficiency of the waste watertreatment can be improved, and energy waste can be reduced.

In the present invention, the degree of the third evaporation isascertained by monitoring the concentration of the liquid obtained inthe third evaporation. Specifically, by controlling the concentration ofthe liquid obtained in the third evaporation within the above-mentionedrange, the sodium sulfate doesn't crystallize and precipitate in thethird evaporation. Here, the concentration of the liquid obtained in thethird evaporation is monitored by measuring the density of the liquid;specifically, the density may be measured with a densitometer.

According to another preferred embodiment of the present invention,before the fifth solid-liquid separation is executed, the thirdconcentrated solution that contains sodium chloride crystal is treatedby cooling to obtain treated solution that contains sodium chloridecrystal; then the treated solution that contains sodium chloride crystalis treated by the fifth solid-liquid separation.

Namely, as shown in FIG. 7, the method for treating waste watercontaining ammonium salts that contains NH₄ ⁺, SO₄ ²⁻, Cl⁻ and Na⁺ inthe present invention comprises the following steps:

1) treating waste water to be treated by second evaporation, to obtainsecond ammonia-containing vapor and second concentrated solution thatcontains sodium sulfate crystal, wherein the waste water to be treatedcontains the waste water containing ammonium salts;2) treating the second concentrated solution that contains sodiumsulfate crystal by third solid-liquid separation, and treating theliquid phase obtained in the third solid-liquid separation by coolingcrystallization, to obtain crystalline solution that contains sodiumsulfate crystal;3) treating the crystalline solution that contains sodium sulfatecrystal by fourth solid-liquid separation, and treating the liquid phaseobtained in the fourth solid-liquid separation by third evaporation, toobtain third ammonia-containing vapor and third concentrated solutionthat contains sodium chloride crystal;4) treating the third concentrated solution that contains sodiumchloride crystal by cooling treatment, to obtain treated solution thatcontains sodium chloride crystal;5) treating the treated solution by fifth solid-liquid separation;wherein the pH of the waste water to be treated is adjusted to a valuegreater than 9, before the waste water to be treated is treated by thesecond evaporation;in relation to 1 mol SO₄ ²⁻ contained in the waste water to be treated,the Cl⁻ contained in the waste water to be treated is 14 mol or less;the second evaporation ensures that the sodium chloride doesn'tcrystallize and precipitate.

Preferably, the third concentrated solution that contains sodiumchloride crystal is third concentrated solution that contains sodiumchloride crystal and sodium sulfate crystal, and the sodium sulfatecrystal in the third concentrated solution that contains sodium chloridecrystal and sodium sulfate crystal is dissolved through the coolingtreatment.

In the present invention, in a case that the cooling treatment is used,the purpose of the third evaporation is to drive the sodium chlorideand/or sodium sulfate to precipitate and evaporate the ammonia further,so as to attain a purpose of separating the ammonia and salts in thewaste water.

According to the present invention, the conditions of the thirdevaporation are controlled so that sodium chloride precipitated first asthe solvent is continuously reduced, and then sodium sulfate mayprecipitate, and third concentrated solution that contains sodiumchloride crystal is obtained. To reduce the quantity of circulatingwater in the treatment system, improve the efficiency of the thirdevaporation and thereby improve the efficiency of the waste watertreatment, the third evaporation preferably is executed to a degree thatboth the sodium chloride and the sodium sulfate precipitate at the sametime, which is to say, preferably third concentrated solution thatcontains sodium sulfate crystal and sodium chloride crystal is obtainedin the third evaporation.

The conditions of the third evaporation may include: temperature: theconditions of the third evaporation include: temperature: 35° C. orabove; pressure: −98 kPa or above; preferably, the conditions of thethird evaporation include: temperature: 45° C.-175° C.; pressure: −95kPa-653 kPa; preferably, the conditions of the third evaporationinclude: temperature: 60° C.-175° C.; pressure: −87 kPa-653 kPa;preferably, the conditions of the third evaporation include:temperature: 75° C.-175° C.; pressure: −73 kPa-653 kPa; preferably, theconditions of the third evaporation include: temperature: 80° C.-130°C.; pressure: −66 kPa-117 kPa; preferably, the conditions of the thirdevaporation include: temperature: 95° C.-110° C.; pressure: −37 kPa-12kPa; preferably, the conditions of the third evaporation include:temperature: 105° C.-107° C.; pressure: −8 kPa-0 kPa.

According to the present invention, for the purpose of improving theefficiency of the waste water treatment, the greater the degree of thethird evaporation is, the better the result is; however, if the degreeof the third evaporation exceeds a certain degree, treated solution thatonly contains sodium chloride crystal can't be obtained through thecooling treatment; in that case, though the crystal may be dissolved,for example, by adding water into the treated solution, the efficiencyof the waste water treatment will be degraded. Therefore, preferably thethird evaporation is executed to a degree that sodium chloride crystaland sodium sulfate crystal precipitate at the same time and the sodiumsulfate crystal in the third concentrated solution that contains sodiumchloride crystal can be dissolved in the cooling treatment; namely,preferably the third concentrated solution that contains sodium chloridecrystal, which is obtained in the step 3), is concentrated solution thatcontains sodium chloride crystal and sodium sulfate crystal, and thesodium sulfate crystal in the concentrated solution that contains sodiumchloride crystal and sodium sulfate crystal is dissolved through thecooling treatment. To ensure that the sodium sulfate crystal in theconcentrated solution that contains sodium chloride crystal and sodiumsulfate crystal can be dissolved in the cooling treatment, for example,the degree of the third evaporation may be controlled so thatconcentration of sodium sulfate in the treated solution is Y′ or lower(wherein Y′ is the concentration of sodium sulfate in the treatedsolution when both sodium sulfate and sodium chloride are saturatedunder the conditions of the cooling treatment). For the purpose ofdriving the sodium chloride to precipitate as far as possible andensuring that the sodium sulfate can be dissolved fully in the follow-upcooling treatment procedure, preferably, through the third evaporation,the concentration of sodium sulfate in the treated solution is0.9Y′-0.99Y′, more preferably is 0.95Y′-0.98Y′. By controlling thedegree of the third evaporation to the above-mentioned range, the sodiumchloride can precipitate as far as possible in the third evaporationprocess, and the sodium sulfate is dissolved fully in the coolingtreatment, so that pure sodium chloride crystal is obtained throughseparation finally. By causing the sodium chloride to crystallize in thethird evaporation as far as possible, the efficiency of the waste watertreatment can be improved, and energy waste can be reduced.

In the present invention, the degree of the third evaporation isascertained by monitoring the amount of evaporation in the thirdevaporation (i.e., the amount of liquid obtained in the thirdevaporation). Specifically, the concentration ratio is controlled bycontrolling the amount of evaporation in the third evaporation (i.e.,the amount of ammonia water), so that the sodium sulfate crystal thatprecipitates in the third concentrated solution obtained in the thirdevaporation can be dissolved in the cooling treatment. Here, the degreeof the third evaporation is monitored by measuring the amount ofevaporation in the third evaporation; specifically, flow measurement maybe performed with a mass flow meter, i.e., the amount of secondary steamor the amount of condensate may be measured.

In the present invention, the purpose of the cooling treatment is todrive the sodium sulfate crystal that is contained possibly in the thirdconcentrated solution that contains sodium chloride crystal to dissolveand drive the sodium chloride to further precipitate. Causing the sodiumsulfate crystal in the third concentrated solution that contains sodiumchloride crystal to dissolve in the cooling treatment process means thatthe degree of the third evaporation must be controlled appropriately toobtain pure sodium chloride crystal, which is to say, the concentrationof sodium sulfate in the mixture system is controlled so that it doesn'texceed the corresponding solubility of sodium sulfate under theconditions of the cooling treatment, without excluding sodium sulfatethat is entrained in the sodium chloride crystal or absorbed to thesurface of the sodium chloride crystal. Owing to the fact that themoisture content in the crystal after solid-liquid separation isdifferent, usually the content of sodium sulfate in the obtained sodiumchloride crystal is 8 mass % or lower (preferably 4 mass % or lower). Inthe present invention, it is deemed that the sodium sulfate crystal isdissolved if the content of sodium sulfate in the obtained sodiumchloride crystal is 8 mass % or lower.

There is no particular restriction on the conditions of the coolingtreatment, as long as the sodium sulfate crystal in the thirdconcentrated solution that contains sodium chloride crystal can be fullydissolved in the cooling treatment process. For example, the conditionsof the cooling treatment may include: temperature: 13° C.-100° C.,preferably 15° C.-45° C., more preferably 15° C.-35° C., furtherpreferably 17.9° C.-35° C. To ensure the effect of the coolingtreatment, preferably, the conditions of the cooling treatment include:time: 5 min. or longer, preferably 5 min.-120 min., more preferably 30min.-90 min.; further preferably 50 min.-60 min.

The specific temperature, time, and device of the cooling treatment maybe the same as those of the cooling treatment in the method in the thirdaspect, and will not be further detailed here.

According to the present invention, to take full advantage of the heatin the third ammonia-containing vapor obtained in the third evaporation,preferably third heat exchange between the fourth mother liquid and thethird ammonia-containing vapor is executed, before the fourth motherliquid is fed into the first MVR evaporation device 1.

According to a preferred embodiment of the present invention, the thirdheat exchange between the fourth mother liquid and the thirdammonia-containing vapor is executed in a third heat exchange device 33and a fourth heat exchange device 34 respectively. Specifically, thefourth mother liquid flows through the third heat exchange device 33 andthe fourth heat exchange device 34 sequentially, and the thirdammonia-containing vapor flows through the fourth heat exchange device34 and the third heat exchange device 33 sequentially, so that thetemperature of the fourth mother liquid is increased to facilitate thefirst evaporation, while the third ammonia-containing vapor is condensedto obtain ammonia water. After the heat exchange in the third heatexchange device 33, the temperature of the fourth mother liquid isincreased to 34° C.-109° C., preferably 44° C.-109° C. After the heatexchange in the fourth heat exchange device 34, the temperature of thefourth mother liquid is increased to 42° C.-117° C., preferably 53°C.-117° C.

According to the present invention, the fifth solid-liquid separationmay be performed in a second solid-liquid separation device 92 (e.g.,centrifugal machine, band filter, or plate and frame filter, etc.).After the fifth solid-liquid separation, the fifth mother liquidobtained in the second solid-liquid separation device 92 (i.e., theliquid phase obtained in the fifth solid-liquid separation) is returnedto the second MVR evaporation device 3 for second evaporation again.Specifically, the fifth mother liquid may be returned by means of theninth circulation pump 79 to a position just before the second pHadjustment. Preferably the solid phase obtained in the fifthsolid-liquid separation is washed by fifth washing.

The fifth solid-liquid separation and the fifth washing may be executedin the same way as the second solid-liquid separation and the secondwashing respectively, and will not be further detailed here. For theliquid produced in the washing, preferably the washing liquid, water orsodium chloride solution washing liquid and the elutriant are returnedto the first MVR evaporation device 1. For example, the liquid may bereturned by means of an tenth circulation pump 80 to the first MVRevaporation device 1.

According to a preferred embodiment of the present invention, the tailgas produced in the cooling crystallization is treated by ammoniaremoval and then exhausted; the residual tail gas after condensation inthe third heat exchange is treated by ammonia removal and thenexhausted; the residual tail gas after condensation in the first heatexchange is treated by ammonia removal and then exhausted. The tail gasproduced in the cooling crystallization is the tail gas exhausted fromthe cooling crystallization device 2, and the residual tail gas aftercondensation in the third heat exchange is the incondensable gasexhausted from the fourth heat exchange device 34; the residual tail gasafter condensation in the first heat exchange is the tail gas exhaustedfrom the eighth heat exchange device 38. By removing ammonia from theabove-mentioned tail gas, the content of pollutants in the tail gas canbe further decreased, so that the tail gas can be vented directly.

In a sixth aspect, the present invention provides a method for treatingwaste water containing ammonium salts that contains NH₄ ⁺, SO₄ ²⁻, Cl⁻and Na⁺ as shown in FIGS. 8-9, which comprises the following steps:

1) treating waste water to be treated by fourth evaporation, to obtainfourth ammonia-containing vapor and fourth concentrated solution thatcontains sodium chloride crystal, wherein the waste water to be treatedcontains the waste water containing ammonium salts;2) treating the fourth concentrated solution that contains sodiumchloride crystal by sixth solid-liquid separation, and treating theliquid phase obtained in the sixth solid-liquid separation by coolingcrystallization, to obtain crystalline solution that contains sodiumsulfate crystal;3) treating the concentrated solution that contains sodium sulfatecrystal by seventh solid-liquid separation;wherein the pH of the waste water to be treated is adjusted to a valueequal to or greater than 9, before the waste water to be treated istreated by the fourth evaporation; in relation to 1 mol SO₄ ²⁻ containedin the waste water to be treated, the Cl⁻ contained in the waste waterto be treated is 7.15 mol or more; the cooling crystallization isexecuted in a way that no sodium chloride crystallizes and precipitates.

Preferably, the waste water to be treated is the waste water containingammonium salts; or the waste water to be treated contains the wastewater containing ammonium salts and the liquid phase obtained in theseventh solid-liquid separation.

More preferably, the waste water to be treated is mixed solution of thewaste water containing ammonium salts and at least a part of the liquidphase obtained in the seventh solid-liquid separation.

The method provided in the present invention can treat waste watercontaining ammonium salts, which contains NH₄ ⁺, SO₄ ²⁻, Cl⁻ and Na⁺,and there is no particular restriction on the waste water containingammonium salts, except that the waste water contains NH₄ ⁺, SO₄ ²⁻, Cl⁻and Na⁺.

In the present invention, there is no particular restriction on theorder of the first heat exchange, the adjustment of pH value of thewaste water to be treated, and the blending process of the waste waterto be treated (in the case that the waste water to be treated containsthe waste water containing ammonium salts and the liquid phase obtainedin the seventh solid-liquid separation, a blending process of the wastewater to be treated is required); in other words, the order may beselected appropriately as required; for example, these procedures may beaccomplished before the waste water to be treated is treated by fourthevaporation.

In the present invention, the purpose of the fourth evaporation is todrive sodium chloride to precipitate or drive sodium chloride and sodiumsulfate to precipitate together, and evaporate ammonia, to attain apurpose of separating the ammonia and salts in the waste water.According to the present invention, by controlling the conditions of thefourth evaporation, sodium chloride precipitates first as the solvent isreduced continuously, and then sodium sulfate precipitates, so thatfourth concentrated solution that contains sodium chloride crystal isobtained (the fourth concentrated solution only contains sodium chloridecrystal or contains sodium chloride crystal and sodium sulfate crystal).

In the present invention, the device used for the fourth evaporation isthe same as that used for the first evaporation, and will not be furtherdetailed here. For example, the fourth evaporation may be executed in afirst MVR evaporation device 1.

In the present invention, there is no particular restriction on theconditions of the fourth evaporation; in other words, the evaporationconditions may be selected appropriately as required, as long as thepurpose of crystallization can be attained. To improve the efficiency ofevaporation, the conditions of the fourth evaporation include:temperature: 35° C. or above; pressure: −98 kPa or above; preferably,the conditions of the evaporation include: temperature: 45° C.-175° C.;pressure: −95 kPa-653 kPa; preferably, the conditions of the fourthevaporation include: temperature: 60° C.-160° C.; pressure: −87 kPa-414kPa; preferably, the conditions of the fourth evaporation include:temperature: 75° C.-150° C.; pressure: −73 kPa-292 kPa; preferably, theconditions of the fourth evaporation include: temperature: 80° C.-130°C.; pressure: −66 kPa-117 kPa; preferably, the conditions of the fourthevaporation include: temperature: 95° C.-110° C.; pressure: −37 kPa-12kPa; preferably, the conditions of the fourth evaporation include:temperature: 105° C.-110° C.; pressure: −23 kPa-12 kPa.

If a multi-effect evaporation device is used for the evaporation, in thecase of co-current feeding or counter-current feeding, the conditions ofthe evaporation refer to the evaporation conditions in the lastevaporator of the multi-effect evaporation device; in the case ofparallel-current feeding, the conditions of the evaporation include theevaporation conditions in each evaporator in the multi-effectevaporation device. In addition, to take full advantage of the heat inthe evaporation process, preferably the temperature difference betweenevery two adjacent evaporators is 5° C.-30° C.; more preferably, thetemperature difference between every two adjacent evaporators in thefirst evaporation is 10° C.-20° C.

In the present invention, the operating pressure of the evaporationpreferably is the saturated vapor pressure of the evaporated feedliquid. In addition, the amount of evaporation in the evaporation may beselected appropriately according to the processing capacity of theapparatus and the amount of the waste water to be treated. For example,the amount of evaporation may be 0.1 m³/h or more (e.g., 0.1 m³/h-500m³/h).

To ensure high-purity sodium chloride crystal can be obtained in thefourth evaporation process, in relation to 1 mol SO₄ ²⁻ contained in thewaste water to be treated, the Cl⁻ contained in the waste water to betreated is 7.15 mol or more, preferably is 8 mol or more, preferably is10 mol or more, preferably is 20 mol or more, more preferably is 30 molor more, e.g., 10-20 mol. Specifically, examples may include: 9.5 mol,10.5 mol, 11 mol, 11.5 mol, 12 mol, 12.5 mol, 13 mol, 13.5 mol, 14 mol,14.5 mol, 15 mol, 15.5 mol, 16 mol, 16.5 mol, 17 mol, 17.5 mol, 18 mol,18.5 mol, 19 mol, 19.5 mol, 20 mol, 21 mol, 22 mol, 23 mol, 25 mol, 27mol, 29 mol, 31 mol, 35 mol, 40 mol, 45 mol, or 50 mol, etc. Bycontrolling the molar ratio of SO₄ ²⁻ to Cl⁻ to the above-mentionedrange, pure sodium chloride crystal can be obtained through theevaporation, and separation of sodium sulfate and sodium chloride can berealized.

According to a preferred embodiment of the present invention, the sodiumsulfate in the waste water to be treated doesn't crystallize andprecipitate in the fourth evaporation (i.e., the sodium sulfate is notover-saturated); preferably, through the fourth evaporation, theconcentration of sodium sulfate in the fourth concentrated solution is Yor lower (preferably 0.9Y-0.99Y, more preferably 0.95Y-0.98Y), where Yis the concentration of sodium sulfate in the fourth concentratedsolution when both sodium chloride and sodium sulfate are saturatedunder the conditions of the fourth evaporation. By controlling thedegree of the fourth evaporation within the above-mentioned range,sodium chloride crystallizes and precipitates as far as possible whilesodium sulfate doesn't precipitate. By increasing the amount ofevaporation as far as possible, the efficiency of the waste watertreatment can be improved, and energy waste can be reduced.

According to another preferred embodiment of the present invention, toreduce the quantity of circulating water in the treatment system,improve the efficiency of the fourth evaporation and thereby improve theefficiency of the waste water treatment, the fourth evaporationpreferably is executed to a degree that both the sodium chloride and thesodium sulfate precipitate at the same time, which is to say, preferablyfourth concentrated solution that contains sodium chloride crystal andsodium sulfate crystal is obtained in the fourth evaporation. In thatcase, in order to obtain high-purity sodium chloride crystal, before thesixth solid-liquid separation is executed, the fourth concentratedsolution that contains sodium chloride crystal is treated by coolingtreatment to obtain treated solution that contains sodium chloridecrystal; then the treated solution that contains sodium chloride crystalis treated by the sixth solid-liquid separation. Here, the methodprovided in the present invention comprises the following steps:

1) treating waste water to be treated by fourth evaporation, to obtainfourth ammonia-containing vapor and fourth concentrated solution thatcontains sodium chloride crystal, wherein the waste water to be treatedcontains the waste water containing ammonium salts;2) treating the fourth concentrated solution that contains sodiumchloride crystal by cooling treatment, to obtain treated solution thatcontains sodium chloride crystal;3) treating the treated solution that contains sodium chloride crystalby sixth solid-liquid separation, and treating the liquid phase obtainedin the sixth solid-liquid separation by cooling crystallization, toobtain crystalline solution that contains sodium sulfate crystal;4) treating the concentrated solution that contains sodium sulfatecrystal by seventh solid-liquid separation.

In the embodiment described above, for the purpose of improving theefficiency of the waste water treatment, the greater the degree of thefourth evaporation is, the better the result is; however, if the degreeof the fourth evaporation exceeds a certain degree, treated solutionthat only contains sodium chloride crystal can't be obtained through thecooling treatment; in that case, though the crystal may be dissolved,for example, by adding water into the treated solution, the efficiencyof the waste water treatment will be degraded. Therefore, preferably thefourth evaporation is executed to a degree that sodium chloride crystaland sodium sulfate crystal precipitate at the same time, i.e.,preferably, the fourth concentrated solution that contains crystal,which is obtained in the step 1), is fourth concentrated solution thatcontains sodium chloride crystal and sodium sulfate crystal, and thesodium sulfate crystal in the fourth concentrated solution that containssodium chloride crystal and sodium sulfate crystal is dissolved throughthe cooling treatment. To ensure that the sodium sulfate crystal in thefourth concentrated solution that contains sodium chloride crystal andsodium sulfate crystal can be dissolved in the cooling treatment, forexample, the degree of the fourth evaporation may be controlled so thatconcentration of sodium sulfate in the treated solution is Y′ or lower(wherein Y′ is the concentration of sodium sulfate in the treatedsolution when both sodium sulfate and sodium chloride are saturatedunder the conditions of the cooling treatment). For the purpose ofdriving the sodium chloride to precipitate as far as possible andensuring that the sodium sulfate can be dissolved fully in the follow-upcooling treatment procedure, preferably, through the fourth evaporation,the concentration of sodium sulfate in the treated solution is0.9Y′-0.99Y′, more preferably is 0.95Y′-0.98Y′. By controlling thedegree of the fourth evaporation to the above-mentioned range, thesodium chloride can precipitate as far as possible in the fourthevaporation process, and the sodium sulfate is dissolved fully in thecooling treatment, so that pure sodium chloride crystal is obtainedthrough separation finally. By increasing the amount of evaporation asfar as possible, the efficiency of the waste water treatment can beimproved, and energy can be saved.

In the present invention, the purpose of the cooling treatment is todrive the sodium sulfate crystal that is contained in the fourthconcentrated solution that contains sodium chloride crystal to dissolveand drive the sodium chloride to further precipitate. Causing the sodiumsulfate crystal in the fourth concentrated solution that contains sodiumchloride crystal to dissolve in the cooling treatment process means thatthe degree of the fourth evaporation must be controlled appropriately toobtain pure sodium chloride crystal, which is to say, the concentrationof sodium sulfate in the mixture system is controlled so that it doesn'texceed the corresponding solubility of sodium sulfate under theconditions of the cooling treatment. Besides, in the cooling treatmentprocess, sodium sulfate crystal may be entrained in the sodium chloridecrystal or absorbed to the surface of the sodium chloride crystal. Inthe present invention, the content of sodium sulfate in the obtainedsodium chloride crystal preferably is 8 mass % or lower, more preferablyis 4 mass % or lower. In the present invention, if the content of sodiumsulfate crystal in the obtained sodium chloride crystal is 8 mass % orlower, it is deemed that the sodium sulfate is dissolved.

There is no particular restriction on the conditions of the coolingtreatment, as long as the sodium sulfate crystal in the fourthconcentrated solution that contains sodium chloride crystal can be fullydissolved in the cooling treatment process. For example, the conditionsof the cooling treatment may include: temperature: 13° C.-100° C.,preferably 16° C.-45° C., more preferably 16.5° C.-35° C., furtherpreferably 17.9° C.-31.5° C.; still further preferably 17.9° C.-25° C.To ensure the effect of the cooling treatment, preferably, theconditions of the cooling treatment include: time: 5 min. or longer,preferably 5 min.-120 min., more preferably 45 min.-90 min.; furtherpreferably 50 min.-70 min.

Examples of the temperature of the cooling treatment may include: 13°C., 14° C., 15° C., 15.5° C., 16° C., 16.5° C., 17° C., 17.5° C., 17.9°C., 18° C., 18.5° C., 19° C., 19.5° C., 20° C., 21° C., 23° C., 25° C.,27° C., 30° C., 31° C., 31.5° C., 32° C., 33° C., 34° C., 35° C., 40°C., 45° C., 50° C., or 55° C., etc.

Examples of the time of the cooling treatment may include: 5 min., 6min., 7 min., 8 min., 10 min., 15 min., 20 min., 25 min., 30 min., 35min., 40 min., 45 min., 50 min., 52 min., 54 min., 56 min., 58 min., 60min., 70 min., 100 min., or 120 min.

According to the present invention, the cooling treatment is executed ina low temperature treatment tank 22. The low temperature treatment tank22 may be the same as the above-mentioned low temperature treatment tank55, and will not be further detailed here.

In the present invention, the degree of the fourth evaporation isascertained by monitoring the amount of evaporation (or amount of thecondensate) in the fourth evaporation or the concentration of the fourthconcentrated solution. Specifically, if the degree of the fourthevaporation is ascertained by measuring the amount of evaporation, theconcentration ratio is controlled by controlling the amount ofevaporation (i.e., the amount of secondary steam or amount of ammoniawater), and the degree of the fourth concentration by evaporation ismonitored by measuring the amount of evaporation, so that the sodiumsulfate crystal precipitating in the fourth concentrated solutionobtained in the fourth evaporation can be dissolved in the coolingtreatment. Specifically, a mass flow meter may be used to measure theflow and thereby measure the amount of the secondary steam; or theamount of the condensate may be measured; if the degree of the fourthevaporation is ascertained by measuring the concentration, the sodiumsulfate in the fourth concentrated solution doesn't crystallize andprecipitate in the fourth evaporation by controlling the concentrationof the fourth concentrated solution obtained in the fourth evaporationwithin the above-mentioned range, and the concentration of the liquidobtained in the fourth evaporation is monitored by measuring thedensity; specifically, a densitometer may be used to measure thedensity.

According to the present invention, to take full advantage of the heatin the fourth ammonia-containing vapor obtained in the fourthevaporation, preferably first heat exchange between the waste water tobe treated and the fourth ammonia-containing vapor is executed, beforethe waste water to be treated is fed into the first MVR evaporationdevice 1. To take full advantage of the heat in the sixth mother liquidand/or the fourth concentrated solution that contains sodium chloridecrystal, more preferably, first heat exchange between the waste water tobe treated and the sixth mother liquid and/or the fourth concentratedsolution that contains sodium chloride crystal is executed before thewaste water to be treated is fed into the first MVR evaporation device1.

According to a preferred embodiment of the present invention, as shownin FIG. 8, the first heat exchange between the waste water to be treatedand the fourth ammonia-containing vapor is executed in a first heatexchange device 31 and a second heat exchange device 32 respectively;the first heat exchange between the waste water to be treated and thefourth concentrated solution that contains sodium chloride crystal isexecuted in a fifth heat exchange device 35. Specifically, the fourthammonia-containing vapor flows through the second heat exchange device32 and the first heat exchange device 31 sequentially, and the fourthconcentrated solution that contains sodium chloride crystal flowsthrough the fifth heat exchange device 35; at the same time, a part ofthe waste water to be treated exchanges heat with the condensate of thefourth ammonia-containing vapor in the first heat exchange device 31,and the remaining part of the waste water to be treated exchanges heatwith the fourth concentrated solution that contains sodium chloridecrystal in the fifth heat exchange device 35; then the two parts ofwaste water to be treated are merged, and the merged waste water to betreated exchanges heat with the fourth ammonia-containing vapor in thesecond heat exchange device 32, so that the temperature of the wastewater to be treated is increased to facilitate evaporation, while thefourth ammonia-containing vapor is condensed to obtain ammonia water,and the temperature of the fourth concentrated solution that containssodium chloride crystal is decreased to facilitate cooling treatment.

According to another preferred embodiment of the present invention, asshown in FIG. 9, the first heat exchange between the waste water to betreated and the fourth ammonium-containing vapor is executed in a firstheat exchange device 31 and a second heat exchange device 32respectively; the first heat exchange between the waste water to betreated and the sixth mother liquid (i.e., the liquid phase obtained insixth solid-liquid separation described below) is executed in a fifthheat exchange device 35. Specifically, the fourth ammonia-containingvapor flows through the second heat exchange device 32 and the firstheat exchange device 31 sequentially, and the sixth mother liquid flowsthrough the fifth heat exchange device 35; at the same time, a part ofthe waste water to be treated exchanges heat with the condensate of thefourth ammonia-containing vapor in the first heat exchange device 31,and the remaining part of the waste water to be treated exchanges heatwith the sixth mother liquid in the fifth heat exchange device 35; thenthe two parts of waste water to be treated are merged, and the mergedwaste water to be treated exchanges heat with the fourthammonia-containing vapor in the second heat exchange device 32, so thatthe temperature of the waste water to be treated is increased tofacilitate evaporation, while the fourth ammonia-containing vapor iscondensed to obtain ammonia water, and the temperature of the sixthmother liquid is decreased to facilitate cooling crystallization.

After the heat exchange in the first heat exchange device 31, thetemperature of the waste water to be treated is increased to 44° C.-174°C., preferably 94° C.-109° C.; after the heat exchange in the fifth heatexchange device 35, the temperature of the waste water to be treated isincreased to 44° C.-174° C., preferably 94° C.-109° C.; after the firstheat exchange in the second heat exchange device 32, the temperature ofthe waste water to be treated is increased to 52° C.-182° C., preferably102° C.-117° C.

According to the present invention, preferably the pH value of the wastewater to be treated is adjusted to a value greater than 9, preferablygreater than 10.8, more preferably is 10.8-11.5, before the waste waterto be treated is treated by the evaporation. Besides, there is noparticular restriction on the upper limit of pH adjustment of the wastewater to be treated. For example, the pH may be 14 or lower, preferablyis 13.5 or lower, more preferably is 13 or lower. By adjusting the pH ofthe waste water to be treated to the above-mentioned range, ammonia canbe fully evaporated in the evaporation process, and thereby the purityof the obtained sodium chloride can be improved.

For example, before the waste water to be treated is treated by theevaporation, the pH value of the waste water to be treated may beadjusted to any of the following values: 9, 9.5, 9.6, 9.7, 9.8, 9.9, 10,10.1, 10.2, 10.3, 10.4, 10.5, 10.6, 10.7, 10.8, 10.9, 11, 11.1, 11.2,11.3, 11.4, 11.5, 11.6, 11.7, 11.8, 11.9, 12, 12.2, 12.4, 12.6, 12.8,13, 13.5, or 14, etc.

In the present invention, there is no particular restriction on the pHadjustment method. For example, the pH value of the waste water to betreated may be adjusted by adding an alkaline substance. There is noparticular restriction on the alkaline substance, as long as thealkaline substance can attain the purpose of adjusting the pH. To avoidintroducing any new impurity into the waste water to be treated andimprove the purity of the obtained crystal, the alkaline substancepreferably is NaOH.

The alkaline substance may be added with a conventional method in theart. However, preferably the alkaline substance is mixed in the form ofwater solution with the waste water to be treated. For example, watersolution that contains the alkaline substance may be charged into apipeline through which the waste water to be treated is inputted. Thereis no particular restriction on the content of the alkaline substance inthe water solution, as long as the water solution can attain the purposeof adjusting the pH. However, to reduce the amount of water and furtherreduce the cost, preferably saturated water solution of the alkalinesubstance or the seventh mother liquid is used. To monitor the pH of thewaste water to be treated, the pH of the waste water to be treated maybe measured after the pH adjustment.

According to a preferred embodiment of the present invention, the fourthevaporation process is performed in the first MVR evaporation device 1.Specifically, before the waste water containing ammonium salts is fedinto the first heat exchange device 31 for the first heat exchange, pHadjustment is made for the first time by introducing the water solutionthat contains an alkaline substance into the pipeline through which thewaste water containing ammonium salts is fed into the first heatexchange device 31 and mixing with the waste water therein; then, pHadjustment is made for the second time by introducing the water solutionthat contains an alkaline substance into the pipeline through which thewaste water to be treated is fed into the first MVR evaporation device1.

Through twice pH adjustments, the pH of the waste water to be treated isadjusted to be greater than 9, preferably greater than 10.8, before thewaste water to be treated is treated by the evaporation. Preferably,through the first pH adjustment, the pH is adjusted to a value greaterthan 7 (preferably is 7-9); through the second pH adjustment, the pH isadjusted to a value greater than 9 (preferably is greater than 10.8).

To detect the pH after the first pH adjustment and the second pHadjustment, preferably a first pH measuring device 61 is provided in thepipeline through which the waste water containing ammonium salts is fedinto the first heat exchange device 31 to measure the pH after the firstpH adjustment, and a second pH measuring device 62 is provided in thepipeline through which the waste water to be treated is fed into thefirst MVR evaporation device 1 to measure the pH after the second pHadjustment.

According to the present invention, the sixth solid-liquid separationmay be performed in a first solid-liquid separation device 91 (e.g.,centrifugal machine, band filter, or plate and frame filter, etc.).After the sixth solid-liquid separation, the sixth mother liquidobtained in the first solid-liquid separation device 91 (i.e., theliquid phase obtained in the sixth solid-liquid separation) is fed intothe cooling crystallization device 2 for cooling crystallization.Specifically, the sixth mother liquid may be fed by means of a sixthcirculation pump 76 into the cooling crystallization device 2. Inaddition, preferably the solid phase obtained in the sixth solid-liquidseparation is washed by sixth washing.

The sixth solid-liquid separation and the sixth washing may be executedin the same way as the second solid-liquid separation and the secondwashing respectively, and will not be further detailed here. The liquidproduced in the washing preferably is returned to the first MVRevaporation device 1. For example, the liquid may be returned by meansof an eighth circulation pump 78 to the first MVR evaporation device 1.

In the present invention, the purpose of the cooling crystallization isto drive the sodium sulfate to precipitate while prevent the sodiumchloride from precipitating, so that the sodium sulfate can be separatedsuccessfully from the waste water. The cooling crystallization onlydrives the sodium sulfate to precipitate, but doesn't exclude sodiumchloride and other substances, which are entrained in the sodium sulfatecrystal or absorbed to the surface of the sodium sulfate crystal. In thepresent invention, preferably the content of sodium sulfate in theobtained sodium sulfate crystal is 92 mass % or higher, more preferablyis 96 mass % or higher, further preferably is 98 mass % or higher. Itshould be understood that the quantity of the obtained sodium sulfatecrystal is measured by dry mass. If the content of sodium sulfate in theobtained sodium sulfate crystal is within the above-mentioned range, itis deemed that only sodium sulfate precipitates.

According to the present invention, the conditions of the coolingcrystallization are the same as the conditions of the coolingcrystallization in the method in the third aspect, and will not befurther detailed here.

According to the present invention, to ensure that sodium sulfatecrystal is obtained in the cooling crystallization, the concentration ofSO₄ ²⁻ in the sixth mother liquid preferably is 0.01 mol/L or higher,more preferably is 0.07 mol/L or higher, further preferably is 0.1 mol/Lor higher, still further preferably is 0.2 mol/L or higher, particularlypreferably is 0.3 mol/L or higher. According to the present invention,to improve the purity of the sodium sulfate crystal obtained in thecooling crystallization, the concentration of Cl⁻ in the sixth motherliquid preferably is 5.2 mol/L or lower, more preferably is 5 mol/L orlower, further preferably is 4.5 mol/L or lower, still furtherpreferably is 4 mol/L or lower.

In the present invention, if the concentration of SO₄ ²⁻ or Cl⁻ in thesixth mother liquid is not within the above-mentioned range, theconcentration may be adjusted before the cooling crystallization isexecuted. Preferably, the concentration is adjusted with the waste watercontaining ammonium salts. Specifically, the waste water containingammonium salts may be mixed with the sixth mother liquid in the firstmother liquid tank 53.

Examples of the content of SO₄ ²⁻ in the sixth mother liquid mayinclude: 0.01 mol/L, 0.03 mol/L, 0.05 mol/L, 0.08 mol/L, 0.1 mol/L, 0.2mol/L, 0.3 mol/L, 0.4 mol/L, 0.5 mol/L, 0.6 mol/L, 0.7 mol/L, 0.8 mol/L,0.9 mol/L, 1 mol/L, 1.1 mol/L, 1.2 mol/L, 1.3 mol/L, 1.4 mol/L, or 1.5mol/L, etc.

In addition, examples of the content of Cl⁻ in the sixth mother liquidmay include: 0.01 mol/L, 0.05 mol/L, 0.1 mol/L, 0.3 mol/L, 0.6 mol/L,0.8 mol/L, 1 mol/L, 1.2 mol/L, 1.4 mol/L, 1.6 mol/L, 1.8 mol/L, 2.0mol/L, 2.2 mol/L, 2.4 mol/L, 2.6 mol/L, 2.8 mol/L, 3 mol/L, 3.2 mol/L,3.4 mol/L, 3.6 mol/L, 3.8 mol/L, 4 mol/L, 4.5 mol/L, or 5 mol/L, etc.

According to the present invention, the cooling crystallization isexecuted in the same way as the cooling crystallization in the method inthe third aspect, and will not be further detailed here.

To detect the pH value after the third pH adjustment, preferably a thirdpH measuring device 63 is provided on the pipeline through which thesixth mother liquid is fed into the third heat exchange device 33 tomeasure the pH value after the third pH adjustment.

In the present invention, preferably the concentration of Cl⁻ in thesixth mother liquid is adjusted as required before the sixth motherliquid is treated by cooling crystallization, so that the concentrationof sodium chloride in the crystalline solution is X or lower, where X isthe concentration of sodium chloride in the crystalline solution whenboth sodium sulfate and sodium chloride are saturated under theconditions of cooling crystallization. Preferably, the concentration ofsodium chloride in the crystalline solution is 0.95X-0.999X. Thus,sodium chloride doesn't precipitate in the cooling crystallizationprocess, and the precipitation ratio of sodium sulfate can be improved.By adjusting the concentration of Cl⁻ in the sixth mother liquid, theconcentration of sodium chloride in the crystalline solution is X orlower, and sodium chloride will not precipitate (the content of sodiumchloride in the obtained crystal is 8 mass % or lower, preferably is 4mass % or lower, more preferably is 3 mass % or lower); thus, theprecipitation ratio of sodium sulfate in the cooling crystallizationprocess is improved, and the efficiency of the cooling crystallizationis improved. The concentration adjustment may be performed with thewaste water containing ammonium salts, the washing liquid after elutingthe sodium sulfate crystal, and sodium sulfate, etc., preferably thewaste water containing ammonium salts is used.

By controlling the cooling crystallization to proceed at theabove-mentioned temperature, Cl⁻ concentration, and pH, sodium sulfatecan precipitate fully while sodium chloride and other substances don'tprecipitate in the cooling crystallization process, so that the purposeof separating and purifying sodium sulfate is attained.

In the present invention, through seventh solid-liquid separation of thecrystalline solution that contains sodium sulfate crystal, sodiumsulfate crystal and seventh mother liquid (i.e., the liquid phaseobtained in the seventh solid-liquid separation) are obtained. There isno particular restriction on the method of the seventh solid-liquidseparation. For example, the method may be selected from one or more ofcentrifugation, filtering, and sedimentation.

According to the present invention, the seventh solid-liquid separationmay be performed in a second solid-liquid separation device 92 (e.g.,centrifugal machine, band filter, or plate and frame filter, etc.).After the seventh solid-liquid separation, the seventh mother liquidobtained in the second solid-liquid separation device 92 is storedtemporarily in second mother liquid tank 54, and may be returned bymeans of a ninth circulation pump 79 into the first MVR evaporationdevice 1 for evaporation. In addition, preferably the solid phaseobtained in the seventh solid-liquid separation is washed by seventhwashing.

The seventh solid-liquid separation and the seventh washing may beexecuted in the same way as the first solid-liquid separation and thefirst washing respectively, and will not be further detailed here. Forthe liquid produced in the washing, preferably the washing liquid (wateror sodium sulfate solution) is returned to the cooling crystallizationdevice 2. For example, the liquid may be returned by means of a tenthcirculation pump 80 to the cooling crystallization device 2.

According to a preferred embodiment of the present invention, after thecrystalline solution that contains sodium sulfate is obtained throughcooling crystallization, solid-liquid separation is executed with asolid-liquid separation device, and the crystal obtained in thesolid-liquid separation is eluted with sodium sulfate solution (theconcentration of the sodium sulfate solution is the concentration ofsodium sulfate in water solution where both sodium chloride and sodiumsulfate are saturated at the temperature corresponding to the sodiumsulfate crystal to be washed), and the liquid obtained in the elution isreturned to the cooling crystallization device 2. Through the washingprocess described above, the purity of the obtained sodium sulfatecrystal can be improved.

According to the present invention, to take full advantage of thecooling capacity of the seventh mother liquid, preferably second heatexchange between the sixth mother liquid and the seventh mother liquidis executed before the sixth mother liquid is treated by coolingcrystallization.

According to a preferred embodiment of the present invention, the secondheat exchange is executed in a third heat exchange device 33;specifically, the sixth mother liquid and the seventh mother liquid flowthrough the third heat exchange device 33 respectively, so that theyexchange heat and thereby the temperature of the sixth mother liquid isdecreased to facilitate cooling crystallization, while the temperatureof the seventh mother liquid is increased to facilitate evaporation.After the heat exchange in the third heat exchange device 33, thetemperature of the sixth mother liquid is −19.7° C.-15.5° C., preferablyis −19° C.-9° C., more preferably is −4° C.-6° C., close to thetemperature of cooling crystallization.

According to the present invention, to facilitate coolingcrystallization, preferably second heat exchange between the sixthmother liquid and refrigerating liquid is executed further. According toa preferred embodiment of the present invention, the heat exchangebetween the sixth mother liquid and the refrigerating liquid is executedin a sixth heat exchange device 36; specifically, the refrigeratingliquid and a mixture of the sixth mother liquid and the cooledcirculating liquid flow through the sixth heat exchange device 36respectively so that they exchange heat with each other, and thereby thetemperature of the mixture of the sixth mother liquid and the cooledcirculating liquid is decreased further to facilitate coolingcrystallization. The refrigerating liquid may be any conventionalrefrigerating medium for cooling in the art, as long as it can cool thesixth mother liquid to a temperature that meets the coolingcrystallization requirement.

To obtain relatively thick ammonia water and improve the purity ofsodium sulfate obtained in the cooling crystallization and theefficiency of the cooling crystallization, preferably the waste water tobe treated is concentrated to obtain fourth ammonia-containing vapor andconcentrated waste water to be treated before the waste water to betreated is treated by the evaporation. Here, the purpose of theconcentration is to obtain ammonia water at relatively highconcentration and control the concentration of the ammonia water moreeasily, and concentrate the waste water to be treated to facilitate thecooling crystallization. There is no particular restriction on thedegree of the concentration, as long as the concentrated waste water tobe treated meets the above-mentioned evaporation requirement. Theconditions and equipment of the concentration are the same as those ofthe follow-up evaporation. However, preferably the temperature of theconcentration is higher than the temperature of the follow-upevaporation, so that the waste water to be treated can be treatedquickly by the evaporation, and thereby the efficiency of theevaporation can be improved while thick ammonia water is obtained.Furthermore, the pH value of the waste water to be treated is adjustedto a value greater than 9, more preferably greater than 10.8, before thewaste water to be treated is concentrated. Here, preferably the pH valueis adjusted by means of NaOH.

By adjusting the pH value of the waste water to a value greater than 9and concentrating the waste water before the waste water is treated bythe evaporation, ammonia water at relatively high concentration can beobtained, the purity of sodium sulfate obtained in the coolingcrystallization can be improved, and the efficiency can be improved.

According to a preferred embodiment of the present invention, the tailgas produced in the cooling crystallization is treated by ammoniaremoval and then exhausted; the residual tail gas after condensation inthe second heat exchange is treated by ammonia removal and thenexhausted. The tail gas produced in the cooling crystallization is thetail gas exhausted from the cooling crystallization device 2, and theresidual tail gas after condensation in the second heat exchange is theincondensable gas exhausted from the second heat exchange device 32. Byremoving ammonia from the above-mentioned tail gas, the content ofpollutants in the tail gas can be further decreased, so that the tailgas can be vented directly.

In the present invention, to improve the salinity of the liquid in theMVR evaporation device and decrease the ammonia content in the liquid,preferably a part of liquid after the evaporation in the MVR evaporationdevice (i.e., liquid in the MVR evaporation device, hereinafter alsoreferred to as circulating liquid) is returned to the MVR evaporationdevice for evaporation, preferably is heated up and then returned to theMVR evaporation device for evaporation. The recirculation ratio ofevaporation in the MVR evaporation device refers to the ratio of therecirculated amount to the difference between the total amount of liquidin the MVR evaporation device and the recirculated amount. Therecirculation ratio may be set appropriately according to the amount ofevaporation, to ensure that the MVR evaporation device can evaporatewater and ammonia in required amounted at the given evaporationtemperature. For example, the recirculation ratio of the firstevaporation may be 10-200, preferably is 40-150; the secondrecirculation ratio of the second evaporation may be 10-200, preferablyis 50-100; the third recirculation ratio of the third evaporation may be10-200, preferably is 50-100; the recirculation ratio of the fourthevaporation may be 10-200, preferably is 40-170.

According to the present invention, preferably, the method furthercomprises compressing the ammonia-containing vapor obtained in the MVRevaporation device before heat exchange is executed. For example, thecompression may be executed by means of compressors 101 and 102. Bycompressing the ammonia-containing vapor, energy is fed into the MVRevaporation system to ensure that the waste water temperaturerise—evaporation—temperature drop process is executed continuously.Initiation steam has to be inputted for initiating the MVR evaporationprocess, but the energy is solely supplied by means of the compressors101 and 102 in the continuous operation state, without any other energyinput. The compressors 101 and 102 may be conventional compressors inthe art, such as centrifugal compressors, turbine compressors, or rootscompressors, etc. Through compression with the compressors 101 and 102,the temperature of the ammonia-containing vapor is increased by 5°C.-20° C.

In the present invention, there is no particular restriction on thefirst heat exchange device 31, the second heat exchange device 32, thethird heat exchange device 33, the fourth heat exchange device 34, thefifth heat exchange device 35, the sixth heat exchange device 36, theeighth heat exchange device 38, and the eleventh heat exchange device30; in other words, different conventional heat exchangers in the artmay be used for those heat exchange devices, as long as the heatexchange devices can attain the purpose of heat exchange. Specifically,the heat exchange unit may be a jacket-type heat exchanger, plate-typeheat exchanger, or shell and tube heat exchanger, etc., preferably is aplate-type heat exchanger. The material of the heat exchanger may beselected as required. For example, to resist erosion of chloride ions, aheat exchanger made of duplex stainless steel, titanium and titaniumalloy, or hastelloy may be selected. At a low temperature, a heatexchanger made of plastic material may be selected; at a hightemperature, a duplex stainless steel plate-type heat exchanger may beselected.

According to a preferred embodiment of the present invention, the tailgas produced in the cooling crystallization is treated by ammoniaremoval and then exhausted; the residual tail gas after condensation inthe second heat exchange is treated by ammonia removal and thenexhausted. The tail gas produced in the cooling crystallization is thetail gas exhausted from the cooling crystallization device 2, and theresidual tail gas after condensation in the second heat exchange is theincondensable gas exhausted from the fourth heat exchange device 34 asshown in FIG. 4; By removing ammonia from the above-mentioned tail gas,the content of pollutants in the tail gas can be further decreased, sothat the tail gas can be vented directly.

As a method for the above-mentioned ammonia removal, the ammonia may beabsorbed in the tail gas absorption tower 83. There is no particularrestriction on the tail gas absorption tower 83; in other words, thetail gas absorption tower 83 may be any conventional absorption tower inthe art, such as plate-type absorption tower, packed absorption tower,falling film absorption tower, or void tower, etc. The tail gasabsorption tower 83 has circulating water in it, the circulating wateris circulated in the tail gas absorption tower 83 under the action ofthe fourth circulation pump 74, or water can be replenished to the tailgas absorption tower 83 by means of the third circulation pump 73 fromthe circulating water tank 82; fresh water can be replenished to thecirculating water tank 82, and thereby the temperature and ammoniacontent of the service water of the vacuum pump 81 can be decreased atthe same time. The tail gas and the circulating water in the tail gasabsorption tower 83 may flow in a counter-current mode or co-currentflow mode, preferably flows in a counter-current mode. The circulatingwater may be replenished with fresh water. To ensure that the tail gascan be absorbed extensively, dilute sulfuric acid may be further addedinto the tail gas absorption tower 83, so as to absorb ammonia and thelike in the tail gas. The circulating water may be reused in theproduction or directly sold as ammonia water or ammonium sulfatesolution after it absorbs the tail gas. The tail gas may be charged intothe tail gas absorption tower 83 by means of the vacuum pump 81.

In the present invention, there is no particular restriction on thewaste water containing ammonium salts, as long as the waste watercontaining ammonium salts is waste water that contains NH₄ ⁺, SO₄ ²⁻,Cl⁻ and Na⁺. In addition, the method provided in the present inventionis especially suitable for treatment of waste water that has high saltcontent. Specifically, the waste water containing ammonium salts in thepresent invention may be waste water from a molecular sieve, alumina oroil refining catalyst production process, or waste water obtained bytreating waste water produced in a molecular sieve, alumina or oilrefining catalyst production process through impurity removal andconcentration as described below, preferably is waste water obtained bytreating waste water produced in a molecular sieve, alumina or oilrefining catalyst production process through impurity removal andconcentration as described below.

The content of NH₄ ⁺ in the waste water containing ammonium salts may be8 mg/L or higher, preferably is 300 mg/L or higher.

The content of Na⁺ in the waste water containing ammonium salts may be510 mg/L or higher, preferably is 1 g/L or higher, more preferably is 2g/L or higher, further preferably is 4 g/L or higher, further preferablyis 8 g/L or higher, further preferably is 16 g/L or higher, furtherpreferably is 32 g/L or higher, further preferably is 40 g/L or higher,further preferably is 50 g/L or higher, still further preferably is 60g/L or higher.

The content of SO₄ ²⁻ in the waste water containing ammonium salts maybe 1 g/L or higher, preferably is 2 g/L or higher, more preferably is 4g/L or higher, further preferably is 8 g/L or higher, further preferablyis 16 g/L or higher, further preferably is 32 g/L or higher, furtherpreferably is 40 g/L or higher, further preferably is 50 g/L or higher,further preferably is 60 g/L or higher, still further preferably is 70g/L or higher.

The content of Cl⁻ in the waste water containing ammonium salts may be970 mg/L or higher, preferably is 2 g/L or higher, further preferably is4 g/L or higher, further preferably is 8 g/L or higher, furtherpreferably is 16 g/L or higher, further preferably is 32 g/L or higher,further preferably is 40 g/L or higher, further preferably is 50 g/L orhigher, still further preferably is 60 g/L or higher.

There is no particular restriction on the upper limits of NH₄ ⁺, SO₄ ²⁻,Cl⁻ and Na⁺ contained in the waste water containing ammonium salts. Inconsideration of the availability of the waste water, the upper limitsof SO₄ ²⁻, Cl⁻ and Na⁺ in the waste water containing ammonium salts are200 g/L or lower respectively, preferably are 150 g/L or lower,preferably are 100 g/L or lower; the upper limit of NH₄ ⁺ in the wastewater containing ammonium salts is 50 g/L or lower, preferably is 40 g/Lor lower, preferably is 30 g/L or lower.

In consideration of reducing the energy consumption of the treatmentprocess, preferably the content of SO₄ ²⁻ contained in the waste watercontaining ammonium salts is 0.01 mol/L or higher (preferably is 0.1mol/L or higher, more preferably is 0.2 mol/L or higher, e.g., 0.2-1.5mol/L); in consideration of improving the purity of the sodium sulfateproduct, the content of Cl⁻ contained in the waste water containingammonium salts is 5.2 mol/L or lower (preferably is 4.7 mol/L or lower,more preferably is 3.5 mol/L or lower, further preferably is 2 mol/L orlower, e.g., 0.5-2 mol/L). By confining the concentration of SO₄ ²⁻ andCl⁻ contained in the waste water containing ammonium salts within theabove-mentioned ranges, pure sodium sulfate crystal can be obtained inthe cooling crystallization process, energy can be saved, and thetreatment process is more economically efficient.

In the present invention, the inorganic salt ions contained in the wastewater containing ammonium salts further include inorganic salt ions suchas Mg²⁺, Ca²⁺, K⁺, Fe³⁺, and rare earth element ions, etc., besides NH₄⁺, SO₄ ²⁻, Cl⁻, and Na⁺. The contents of the inorganic salt ions (e.g.,Mg²⁺, Ca²⁺, K⁺, Fe³⁺, and rare earth element ions, etc.) preferably are100 mg/L or lower respectively, more preferably are 50 mg/L or lowerrespectively, further preferably are 10 mg/L or lower respectively,particularly preferably there is no other inorganic salt ion. Byconfining the contents of other inorganic salt ions in the above ranges,the purity of the sodium sulfate crystal and sodium chloride crystalobtained finally can be further improved. To reduce the contents ofother inorganic salt ions in the waste water containing ammonium salts,preferably impurity removal is performed as described below.

The TDS in the waste water containing ammonium salts may be 1.6 g/L orhigher, preferably is 4 g/L or higher, more preferably is 8 g/L orhigher, further preferably is 16 g/L or higher, further preferably is 32g/L or higher, further preferably is 40 g/L or higher, furtherpreferably is 50 g/L or higher, further preferably is 60 g/L or higher,further preferably is 100 g/L or higher, further preferably is 150 g/Lor higher, still further preferably is 200 g/L or higher.

In the present invention, the pH of the waste water containing ammoniumsalts preferably is 4-7, such as 5.8-6.6.

In addition, in view that the COD in the waste water may cause themembrane clogged in the concentration process and has adverse effect tothe purity and color, etc. of the salts during evaporation andcrystallization, the COD in the waste water containing ammonium saltsshould be low as far as possible (preferably is 20 mg/L or lower, morepreferably is 10 mg/L or lower). Preferably the COD is removed byoxidization during pre-treatment. Specifically, the COD may be removedthrough a biological process or advanced oxidization process, etc. Ifthe COD content is very high, preferably an oxidizer is used foroxidization, and the oxidizer may be Fenton reagent, for example.

In the present invention, to decrease the concentration of impurity ionsin the waste water, ensure continuous and stable operation of thetreatment process, and reduce equipment operation and maintenance cost,preferably the impurities in the waste water containing ammonium saltsare removed before the treatment is executed with the treatment methodprovided in the present invention. Preferably, the impurity removalmethod is selected from one or more of solid-liquid separation, chemicalprecipitation, adsorption, ion exchange, and oxidization.

The solid-liquid separation may be executed by filtering,centrifugation, or sedimentation, etc.; the chemical precipitation maybe executed by pH adjustment, carbonate precipitation, or magnesium saltprecipitation, etc.; the adsorption may be executed by physicaladsorption and/or chemical adsorption, and the specific adsorbent may beselected from active carbon, silica gel, alumina, molecular sieve, andnatural clay, etc.; the ion exchange may be executed with any one ofstrong acidic cationic resins and weak acidic cationic resins; theoxidization may be executed with any conventional oxidizer in the art,such as ozone, hydrogen peroxide solution, or potassium permanganate,etc., and preferably is executed with ozone or hydrogen peroxidesolution, etc., to avoid introduction of any new impurity.

The specific impurity removal method may be selected according to thetypes of impurities contained in the waste water containing ammoniumsalts. Suspended substances may be removed by solid-liquid separation;inorganic substances and organic substances may be removed by chemicalprecipitation, ion-exchange, or adsorption, such as weak acidic cationexchange or active carbon adsorption, etc.; organic substances may beremoved by adsorption and/or oxidization, preferably are removed byozone biological activated carbon adsorption and oxidization. Accordingto a preferred embodiment of the present invention, impurities in thewaste water containing ammonium salts are removed by filtering, weakacidic cation exchange, and ozone biological activated carbon adsorptionand oxidization sequentially. Through the above impurity removalprocess, the majority of suspended substances, hardness, silica andorganic substances can be removed, the scaling risk can be decreased,and the wastewater treatment process can operate continuously andstably.

In the present invention, if the waste water has relatively low saltcontent, the waste water containing ammonium salts may be treated byconcentration so that the salt content reaches the range required forthe waste water containing ammonium salts in the present invention,before the treatment is executed with the treatment method provided inthe present invention. Preferably, the concentration method is selectedfrom ED membrane concentration and/or reverse osmosis; more preferably,the concentration is executed through ED membrane concentration andreverse osmosis, and there is no particular restriction on the order ofthe ED membrane concentration and reverse osmosis. The apparatuses andconditions of the ED membrane concentration and reverse osmosistreatment may be conventional ones in the art, and may be selectedaccording to the specific condition of the waste water to be treated.Specifically, the ED membrane concentration may be executed in aunidirectional electrodialysis system or reverse electrodialysis system;the reverse osmosis may be executed with spiral-wound membrane, flatsheet membrane, disc tubular membrane, and vibrating membrane, or acombination of them. Through the concentration, the waste watertreatment efficiency can be improved, and energy waste incurred by highevaporation load can be avoided.

In a preferred embodiment of the present invention, the waste watercontaining ammonium salts is waste water obtained through treating thewaste water produced in a molecular sieve production process by impurityremoval through chemical precipitation, filtering, weak acidic cationexchange and ozone biological activated carbon adsorption andoxidization, concentration with ED membrane, and concentration throughreverse osmosis.

The conditions of the above-mentioned chemical precipitation preferablyare: sodium carbonate is used as a treating agent, sodium carbonate isadded in a quantity of 1.2-1.4 mol in relation to 1 mol calcium ion inthe waste water, the pH of the waste water is adjusted to 7, thereaction temperature is 20-35° C., and the reaction time is 0.5-4 h.

The conditions of the above-mentioned filtering preferably are: thefiltering unit is a multi-media filter that employs double layers offiltering media composed of blind coal and quartz sand, the blind coalis in 0.7-1.7 mm particle size, the quartz sand is in 0.5-1.3 mmparticle size, and the filtering speed is 10-30 m/h. The filtering mediaare regenerated through an “air backwashing—air-water backwashing—waterbackwashing” regeneration process, and the regeneration period is 10-15h.

The conditions of the above-mentioned weak acidic cation exchangepreferably are: pH range: 6.5-7.5; the temperature: ≤40° C., height ofthe resin layer: 1.5-3.0 m, HCl concentration in the regenerated liquid:4.5-5 mass %; dose of regenerant (measured in 100%): 50-60 kg/m³ wetresin; regeneration liquid HCl flow speed: 4.5-5.5 m/h, regenerationcontact time: 35-45 min.; washing flow speed: 18-22 m/h, washing time:2-30 min.; operation flow speed: 15-30 m/h; the acidic cation resin maybe SNT D113 acidic cation resin from Langfang Sanat Chemical Co., Ltd.,for example.

The conditions of the above-mentioned ozone biological activated carbonadsorption and oxidization preferably are: ozone retention time: 50-70min.; empty bed filtering speed: 0.5-0.7 m/h.

The conditions of the above-mentioned ED membrane concentrationpreferably are: current: 145-155 A, voltage: 45-65V. The ED membrane maybe ED membrane from Astom (a Japanese company), for example.

The conditions of the above-mentioned reverse osmosis preferably are:operating pressure: 5.4-5.6 MPa, inlet temperature: 25-35° C., pH:6.5-7.5. The reverse osmosis membrane may be TM810C seawaterdesalination membrane from Toray Bluestar Membrane Co., Ltd., forexample.

According to the present invention, the waste water treatment may becommenced directly with the waste water containing ammonium salts. Ifthe ion contents in the waste water containing ammonium salts meet theconditions specified in the present invention, the waste water treatmentcan be performed with the method described in the present invention; ifthe ion contents in the waste water containing ammonium salts don't meetthe conditions specified in the present invention, the evaporation orcooling crystallization in the second step may be executed first, andthe mother liquid obtained through the solid-liquid separation may bemixed with the waste water containing ammonium salts to adjust the ioncontents in the waste water to be treated to the ranges specified in thepresent invention, and then the waste water treatment may be performedwith the method described in the present invention. Of course,alternatively the ion contents in the waste water to be treated may beadjusted with sodium sulfate or sodium chloride in the initial stage, aslong as the waste water to be treated can meet the requirements for thecontents of SO₄ ²⁻ and Cl⁻ in the waste water to be treated in thepresent invention.

Hereunder the present invention will be detailed in embodiments.

In the following embodiments, the waste water containing ammonium saltsis waste water obtained through treating the waste water produced in azeolite production process sequentially by impurity removal throughchemical precipitation, filtering, weak acidic cation exchange and ozonebiological activated carbon adsorption and oxidization, concentrationwith ED membrane, and concentration through reverse osmosissequentially.

Embodiment 1

As shown in FIG. 4, waste water containing ammonium salts (containing 40g/L NaCl, 120 g/L Na₂SO₄, 7 g/L NH₄Cl, 21.3 g/L (NH₄)₂SO₄, with pH=5.8)is fed at 10 m³/h feed rate into the pipeline of the treatment system,45.16 mass % sodium hydroxide solution is introduced into the pipelinefor the first pH adjustment, the resultant mixture in the pipeline ismixed with the second mother liquid returned by means of the ninthcirculation pump 79 to obtain waste water to be treated (the measuredconcentration of Cl⁻ is 1.752 mol/L, and the measured concentration ofSO₄ ²⁻ is 0.897 mol/L), the adjusted pH value is monitored with thefirst pH measuring device 61 (a pH meter) (the measured value is 8);then the waste water to be treated is fed by means of the firstcirculation pump 71 into the second heat exchange device 32 (a plasticheat exchanger) to exchange heat with the first mother liquid, so thatthe temperature of the waste water to be treated is decreased to 9° C.;next, the waste water is mixed with the cooled circulating liquid fedfrom the cooling crystallization device 2 (a freezing crystallizationtank) by means of the second circulation pump 72, the resultant mixtureexchanges heat with the refrigerating liquid in the sixth heat exchangedevice 36, so that the temperature of the mixture is further decreased;then, the mixture is fed into the cooling crystallization device 2 andtreated by cooling crystallization, so that crystalline solution thatcontains sodium sulfate crystal is obtained. Wherein the temperature ofthe cooling crystallization is −2° C., and the time of the coolingcrystallization is 150 min., the recirculated amount of the cooledcirculating liquid is controlled to be 1,190 m³/h, and the degree ofsuper-saturation of sodium sulfate in the cooling crystallizationprocess is controlled so that it is not greater than 1.1 g/L.

The crystalline solution that contains sodium sulfate crystal is fedinto the first solid-liquid separation device 91 (a centrifugal machine)for solid-liquid separation; thus, 9.733 m³ first mother liquid thatcontains 166.8 g/L NaCl, 39 g/L Na₂SO₄, 0.43 g/L NaOH, and 7.85 g/L NH₃is obtained per hour and is stored temporarily in the first motherliquid tank 53; in addition, 5,043.6 kg filter cake of sodium sulfatedecahydrate crystal at 99 mass % purity, which contains 76 mass % water,is obtained per hour.

The first mother liquid is fed by means of the sixth circulation pump 76into the second heat exchange device 32 for heat exchange, and then isfed into the concentration device 9 for concentration byelectrodialysis, wherein the flow rate of the thick solution in theconcentration is 7.577 m³/h, and the thick solution contains 192.86 g/LNaCl, 45.09 g/L Na₂SO₄, and 9.081 g/L NH₃; next, the thick solution isevaporated by first evaporation, wherein the flow rate of the thinsolution in the concentration is 2.156 m³/h, the thin solution contains75.28 g/L NaCl, 17.60 g/L Na₂SO₄, and 3.54 g/L NH₃, and the thin liquidin the concentration is returned as waste water containing ammoniumsalts.

The first evaporation process is executed in the first MVR evaporationdevice 1 (a falling film+forced circulation two-stage MVR evaporatingcrystallizer). A part of the thick solution obtained throughconcentration of the first mother liquid is fed into the third heatexchange device 33 (a duplex stainless steel plate-type heat exchanger)to exchange heat with the first ammonium-containing vapor after thecompression, the remaining part of the thick solution is fed into thefifth heat exchange device 35 (a duplex stainless steel plate-type heatexchanger) to exchange heat with the first concentrated solution thatcontains sodium sulfate crystal and sodium chloride crystal; then thetwo parts of the thick solution in the concentration are merged, and themerged solution is fed into the fourth heat exchange device 34 (a duplexstainless steel plate-type heat exchanger) to exchange heat with thefirst ammonium-containing vapor, and then is fed into the pipeline ofthe first MVR evaporation device 1; next, 45.16 mass % sodium hydroxidesolution is introduced into the pipeline for pH adjustment, and theadjusted pH is monitored with the second pH measuring device 62 (a pHmeter) (the measured value is 11); then the mixture is treated by firstevaporation in the first MVR evaporation device 1, to obtain firstconcentrated solution that contains sodium sulfate crystal and sodiumchloride crystal and first ammonium-containing vapor. The temperature ofthe first evaporation is 105° C., the pressure is −7.02 kPa, and theamount of evaporation is 5.657 m³/h. After the first ammonium-containingvapor is compressed by the compressor 102 (the temperature is increasedby 19° C.), it exchanges heat with the first mother liquid in the fourthheat exchange device 34 and the third heat exchange device 33sequentially, so that first ammonia water is obtained, and is stored inthe second ammonia water storage tank 52. In addition, to improve thesolid content in the first MVR evaporation device 1, a part of theliquid after the first evaporation in the first MVR evaporation device 1is circulated as circulating liquid by means of the seventh circulationpump 77 to the first MVR evaporation device 1 again for firstevaporation (the recirculation ratio is 51.3). The degree of the firstevaporation is monitored with the mass flow meter provided on the firstMVR evaporation device 1, to control the amount of evaporation in thefirst evaporation to 3.523 m³/h (equivalent to controlling theconcentration of sodium sulfate in the treated solution to 0.9787Y (278g/L)).

The first concentrated solution that contains sodium sulfate crystal andsodium chloride crystal, which is obtained in the first evaporation, istreated by cooling treatment in the low temperature treatment tank 55(temperature: 17.9° C., time: 50 min.) to obtain treated solution thatcontains sodium chloride crystal. A stirring paddle is provided in thelow temperature treatment tank 55 and operates at 60 r/min. rotationspeed.

The treated solution that contains sodium chloride crystal is fed intothe second solid-liquid separation device 92 (a centrifugal machine) forsecond solid-liquid separation, 3.3 m³ second mother liquid thatcontains 278 g/L NaCl, 92 g/L Na₂SO₄, 2.2 g/L NaOH and 0.37 g/L NH₃ isobtained per hour, and the second mother liquid is temporarily stored inthe second mother liquid tank 54. The obtained solid sodium chloride(492.80 kg filter cake of sodium chloride crystal with 15 mass % watercontent is obtained per hour, wherein the content of sodium sulfate is1.5 mass % or lower) is eluted with 278 g/L sodium chloride solution inthe same dry mass as the sodium chloride, and is dried in a drier, thus418.87 kg sodium chloride (at 99.5 mass % purity) is obtained per hour;the second washing liquid obtained in the washing is returned by meansof the tenth circulation pump 80 to the first MVR evaporation device 1.

In this embodiment, 3.523 m³ first ammonia water at 1.9 mass %concentration is obtained per hour in the second ammonia water storagetank 52.

In addition, the tail gas discharged from the cooling crystallizationdevice 2 and the fourth heat exchange device is introduced by means ofthe vacuum pump 81 into the tail gas absorption tower 83 for absorption.The tail gas absorption tower 83 has circulating water in it, thecirculating water is circulated in the tail gas absorption tower 83under the action of the fourth circulation pump 74, and water isreplenished to the tail gas absorption tower 83 by means of the thirdcirculation pump 73 from the circulating water tank 82 at the same time;in addition, fresh water is replenished to the circulating water tank82, and thereby the temperature and ammonia content of the service waterof the vacuum pump 81 are decreased. Dilute sulfuric acid is furthercharged into the tail gas absorption tower 83 to absorb ammonia or thelike in the tail gas. The MVR evaporation is initiated by charging steamat 143.3° C. temperature in the initial stage.

Embodiment 2

The waste water containing ammonium salts is treated with the methoddescribed in the embodiment 1, but: waste water containing ammoniumsalts that contains 68 g/L NaCl, 100 g/L Na₂SO₄, 6 g/L NH₄Cl and 9 g/L(NH₄)₂SO₄ with pH=6.5 is treated, the concentration of Cl⁻ is 2.219mol/L, and the concentration of SO₄ ²⁻ is 0.723 mol/L in the obtainedwaste water to be treated. After the heat exchange in the second heatexchange device 32, the temperature of the waste water to be treated is7.6° C.

The temperature of the cooling crystallization is 0° C., and the time is150 min.; the temperature of the first evaporation is 100° C., thepressure is −22.83 kPa, and the amount of evaporation is 5.055 m³/h; thetemperature of the cooling treatment is 20° C., and the time is 55 min.

3,500.8 kg filter cake of sodium sulfate decahydrate crystal with 76mass % water content (at 98.3 mass % purity) is obtained per hour in thefirst solid-liquid separation device 91; 11.344 m³ first mother liquidat concentrations of 183.7 g/L NaCl, 37.5 g/L Na₂SO₄, and 3.68 g/L NH₃is obtained per hour.

In the concentration by electrodialysis, the thick solution in theconcentration is at 8.73 m³/h flow rate, and contains 190.96 g/L NaCl,38.98 g/L Na₂SO₄, and 6.58 g/L NH₃; the thin liquid in the concentrationis at 2.613 m³/h flow rate, and contains 75.73 g/L NaCl, 16.27 g/LNa₂SO₄, and 1.6 g/L NH₃.

776 kg filter cake of sodium chloride crystal with 14.5 mass % watercontent is obtained per hour in second solid-liquid separation device92, and finally 663 kg sodium chloride (at 99.5 mass % purity) isobtained per hour; 11.343 m³ second mother liquid at concentrations of280 g/L NaCl, 89 g/L Na₂SO₄, 2.2 g/L NaOH, and 0.17 g/L NH₃ is obtainedper hour.

5.055 m³ first ammonia water at 0.7 mass % concentration is obtained perhour in the second ammonia water storage tank 52, and the first ammoniawater may be reused in a zeolite production process.

Embodiment 3

The waste water containing ammonium salts is treated with the methoddescribed in the embodiment 1, but: waste water containing ammoniumsalts that contains 70 g/L NaCl, 36 g/L Na₂SO₄, 20 g/L NH₄Cl and 10.45g/L (NH₄)₂SO₄ with pH=6.6 is treated, the concentration of Cl⁻ is 2.557mol/L, and the concentration of SO₄ ²⁻ is 0.404 mol/L in the obtainedwaste water to be treated. After the heat exchange in the second heatexchange device 32, the temperature of the waste water to be treated is−1° C.

The temperature of the cooling crystallization is −4° C., and the timeis 120 min.; the temperature of the first evaporation is 110° C., thepressure is 11.34 kPa, and the amount of evaporation is 6.262 m³/h; thetemperature of the cooling treatment is 25° C., and the time is 60 min.

555.4 kg filter cake of sodium sulfate decahydrate crystal with 76 mass% water content (at 99.5 mass % purity) is obtained per hour in thefirst solid-liquid separation device 91; 14.823 m³ first mother liquidat concentrations of 175.87 g/L NaCl, 33.5 g/L Na₂SO₄, and 6.04 g/L NH₃is obtained per hour.

In the concentration by electrodialysis, the thick solution in theconcentration is at 10.89 m³/h flow rate, and contains 191.47 g/L NaCl,36.47 g/L Na₂SO₄, and 9.46 g/L NH₃; the thin liquid in the concentrationis at 3.93 m³/h flow rate, and contains 66.33 g/L NaCl, 12.63 g/LNa₂SO₄, and 2.28 g/L NH₃.

975.1 kg filter cake of sodium chloride crystal with 15 mass % watercontent is obtained per hour in second solid-liquid separation device92, and finally 828.8 kg sodium chloride (at 99.5 mass % purity) isobtained per hour; 4.815 m³ second mother liquid at concentrations of280.5 g/L NaCl, 82.5 g/L Na₂SO₄, 2.2 g/L NaOH, and 0.29 g/L NH₃ isobtained per hour.

6.26 m³ first ammonia water at 1.25 mass % concentration is obtained perhour in the second ammonia water storage tank 52, and the first ammoniawater may be reused in a zeolite production process.

Embodiment 4

As shown in FIG. 5, waste water containing ammonium salts (containing 38g/L NaCl, 100 g/L Na₂SO₄, 10 g/L NH₄Cl, 26.75 g/L (NH₄)₂SO₄, withpH=6.2) is fed at 10 m³/h feed rate into the pipeline of the treatmentsystem, and then is mixed with the second mother liquid returned by theninth circulation pump 79 to obtain waste water to be treated (themeasured concentration of Cl⁻ is 2.42 mol/L, and the measuredconcentration of SO₄ ²⁻ is 0.689 mol/L); 45.16 mass % sodium hydroxidesolution is introduced into the pipeline for the first pH adjustment,and the adjusted pH value is monitored with the first pH measuringdevice 61 (a pH meter) (the measured value is 8); then the waste waterto be treated is fed by means of the first circulation pump 71 into thesecond heat exchange device 32 (a plastic heat exchanger) to have firstheat exchange with the first mother liquid, so that the temperature ofthe waste water to be treated is decreased to 3° C.; next, the wastewater is mixed with the circulating liquid fed from the coolingcrystallization device 2 (a freezing crystallization tank) by means ofthe second circulation pump 72, the resultant mixture exchanges heatwith the refrigerating liquid in the sixth heat exchange device 36, sothat the temperature of the mixture is further decreased; then, themixture is fed into the cooling crystallization device 2 and treated bycooling crystallization, so that crystalline solution that containssodium sulfate crystal is obtained. Wherein the temperature of thecooling crystallization is −4° C., and the time of the coolingcrystallization is 120 min., the recirculated amount in the coolingcrystallization is controlled to be 1,137 m³/h, and the degree ofsuper-saturation of sodium sulfate in the cooling crystallizationprocess is controlled so that it is not greater than 1 g/L. Thecrystalline solution that contains sodium sulfate crystal is fed intothe first solid-liquid separation device 91 (a centrifugal machine) forsolid-liquid separation; thus, 13.69 m³ first mother liquid thatcontains 200.8 g/L NaCl, 27.5 g/L Na₂SO₄, and 5.4 g/L NH₃ is obtainedper hour and is stored temporarily in the first mother liquid tank 53;in addition, 3,389.91 kg filter cake of sodium sulfate decahydratecrystal at 98.4 mass % purity, which contains 75 mass % water, isobtained per hour.

The first mother liquid is fed by means of the sixth circulation pump 76into the second heat exchange device 32 for heat exchange, and then isfed into the concentration device 9 (a electrodialysis device) forconcentration by electrodialysis, wherein the flow rate of the thicksolution in the concentration is 10.87 m³/h, and the thick solutioncontains 202.3 g/L NaCl, 27.7 g/L Na₂SO₄, and 7.7 g/L NH₃; next, thethick solution is evaporated by first evaporation, wherein the flow rateof the thin solution in the concentration is 2.82 m³/h, the thinsolution contains 97.5 g/L NaCl, 13.3 g/L Na₂SO₄, and 3.5 g/L NH₃, andthe thin liquid in the concentration is returned as waste watercontaining ammonium salts.

The first evaporation process is executed in the first MVR evaporationdevice 1 (a falling film+forced circulation two-stage MVR evaporatingcrystallizer). The thick solution in the concentration is fed into thethird heat exchange device 33 (a duplex stainless steel plate-type heatexchanger) to exchange heat with the condensate of the firstammonium-containing vapor; then the resultant mixture is fed into thefourth heat exchange device 34 (a duplex stainless steel plate-type heatexchanger) to exchange heat with the first ammonium-containing vaporafter compression, and then is fed into the pipeline of the first MVRevaporation device 1, and sodium hydroxide solution at 45.16 mass %concentration is introduced into the pipeline to adjust the pH value,the adjusted pH value is monitored with the second pH measuring device62 (a pH meter) (the measured value is 10.8); then the mixture isevaporated by the first evaporation in the first MVR evaporation device1, so that first concentrated solution that contains sodium chloridecrystal and first ammonium-containing vapor is obtained. The temperatureof the first evaporation is 100° C., the pressure is −22.83 kPa, and theamount of evaporation is 5.12 m³/h. After the first ammonium-containingvapor is compressed by the compressor 102 (the temperature is increasedby 16° C.), it exchanges heat with the first mother liquid in the fourthheat exchange device 34 and the third heat exchange device 33sequentially, so that first ammonia water is obtained, and is stored inthe second ammonia water storage tank 52. In addition, to improve thesolid content in the first MVR evaporation device 1, a part of theliquid after the first evaporation in the first MVR evaporation device 1is circulated as circulating liquid by means of the seventh circulationpump 77 to the first MVR evaporation device 1 again for firstevaporation (the recirculation ratio is 46.3). The degree of the firstevaporation is monitored with the densitometer provided on the first MVRevaporation device 1, to control the concentration of sodium sulfate inthe first concentrated solution to be 0.9626Y (51.5 g/L).

The first concentrated solution that contains sodium chloride crystal,which is obtained in the first evaporation, is fed into the secondsolid-liquid separation device 92 (a centrifugal machine) for secondsolid-liquid separation, 5.85 m³ second mother liquid that contains309.1 g/L NaCl, 51.5 g/L Na₂SO₄, 1.4 g/L NaOH and 0.27 g/L NH₃ isobtained per hour, and the second mother liquid is temporarily stored inthe second mother liquid tank 54; second mother liquid may betransferred by means of the ninth circulation pump 79 to the pipelineinto which the waste water containing ammonium salts is introduced, andis mixed with the waste water containing ammonium salts to obtain wastewater to be treated. The obtained solid sodium chloride (498.83 kgfilter cake of sodium chloride crystal with 14 mass % water content isobtained per hour, wherein the content of sodium sulfate is 2.0 mass %or lower) is eluted with 309 g/L sodium chloride solution in the samedry mass as the sodium chloride, and is dried in a drier, thus 428.99 kgsodium chloride (at 99.5 mass % purity) is obtained per hour; the secondwashing liquid obtained in the washing is returned by means of the tenthcirculation pump 80 to the first MVR evaporation device 1.

In this embodiment, 5.12 m³ first ammonia water at 1.7 mass %concentration is obtained per hour in the second ammonia water storagetank 52.

In addition, the tail gas discharged from the cooling crystallizationdevice 2 and the fourth heat exchange device is introduced by means ofthe vacuum pump 81 into the tail gas absorption tower 83 for absorption.The tail gas absorption tower 83 has circulating water in it, thecirculating water is circulated in the tail gas absorption tower 83under the action of the fourth circulation pump 74, and water isreplenished to the tail gas absorption tower 83 by means of the thirdcirculation pump 73 from the circulating water tank 82 at the same time;in addition, fresh water is replenished to the circulating water tank82, and thereby the temperature and ammonia content of the service waterof the vacuum pump 81 are decreased. Dilute sulfuric acid is furthercharged into the tail gas absorption tower 83 to absorb ammonia or thelike in the tail gas. The MVR evaporation is initiated by charging steamat 143.3° C. temperature in the initial stage.

Embodiment 5

The waste water containing ammonium salts is treated with the methoddescribed in the embodiment 4, but: waste water containing ammoniumsalts that contains 46 g/L NaCl, 96 g/L Na₂SO₄, 12 g/L NH₄Cl and 25.5g/L (NH₄)₂SO₄ with pH=6.6 is treated, the concentration of Cl⁻ is 2.43mol/L, and the concentration of SO₄ ²⁻ is 0.687 mol/L in the obtainedwaste water to be treated. After the heat exchange in the second heatexchange device 32, the temperature of the waste water to be treated is5° C.

The temperature of the cooling crystallization is −2° C., and the timeis 125 min.; the temperature of the first evaporation is 75° C., thepressure is −72.74 kPa, and the amount of evaporation is 5.32 m³/h.

3,446.63 kg filter cake of sodium sulfate decahydrate crystal with 76mass % water content (at 98.6 mass % purity) is obtained per hour in thefirst solid-liquid separation device 91; 13.17 m³ first mother liquid atconcentrations of 202.8 g/L NaCl, 29.8 g/L Na₂SO₄, and 7.8 g/L NH₃ isobtained per hour.

In the concentration by electrodialysis, the thick solution in theconcentration is at 10.65 m³/h flow rate, and contains 200.5 g/L NaCl,29.5 g/L Na₂SO₄, and 8.3 g/L NH₃; the thin liquid in the concentrationis at 2.51 m³/h flow rate, and contains 106.3 g/L NaCl, 15.6 g/L Na₂SO₄,and 4.0 g/L NH₃.

615.44 kg filter cake of sodium chloride crystal with 15 mass % watercontent is obtained per hour in second solid-liquid separation device92, and finally 523.12 kg sodium chloride (at 99.5 mass % purity) isobtained per hour; 5.45 m³ second mother liquid at concentrations of305.3 g/L NaCl, 57.6 g/L Na₂SO₄, 0.50 g/L NaOH, and 0.3 g/L NH₃ isobtained per hour in the second solid-liquid separation device 92. 5.32m³ first ammonia water at 1.6 mass % concentration is obtained per hourin the second ammonia water storage tank 52, and the first ammonia watermay be reused in a zeolite production process.

Embodiment 6

The waste water containing ammonium salts is treated with the methoddescribed in the embodiment 4, but: waste water containing ammoniumsalts that contains 33 g/L NaCl, 90 g/L Na₂SO₄, 10 g/L NH₄Cl and 27.7g/L (NH₄)₂SO₄ with pH=6.3 is treated, the concentration of Cl⁻ is 2.177mol/L, and the concentration of SO₄ ²⁻ is 0.693 mol/L in the obtainedwaste water to be treated. After the heat exchange in the second heatexchange device 32, the temperature of the waste water to be treated is3° C.

The temperature of the cooling crystallization is −4° C., and the timeis 120 min.; the temperature of the first evaporation is 50° C., thepressure is −92.67 kPa, and the amount of evaporation is 4.61 m³/h.

3,197.06 kg filter cake of sodium sulfate decahydrate crystal with 74.5mass % water content (at 98.9 mass % purity) is obtained per hour in thefirst solid-liquid separation device 91; 13.38 m³ first mother liquid atconcentrations of 178.6 g/L NaCl, 32.5 g/L Na₂SO₄, and 7.6 g/L NH₃ isobtained per hour.

In the concentration by electrodialysis, the thick solution in theconcentration is at 9.83 m³/h flow rate, and contains 194.6 g/L NaCl,35.4 g/L Na₂SO₄, and 5.5 g/L NH₃; the thin liquid in the concentrationis at 3.56 m³/h flow rate, and contains 67.2 g/L NaCl, 12.2 g/L Na₂SO₄,and 2.8 g/L NH₃.

456.92 kg filter cake of sodium chloride crystal with 15 mass % watercontent is obtained per hour in second solid-liquid separation device92, and finally 388.38 kg sodium chloride (at 99.5 mass % purity) isobtained per hour; 5.30 m³ second mother liquid at concentrations of294.7 g/L NaCl, 65.7 g/L Na₂SO₄, 0.14 g/L NaOH, and 0.3 g/L NH₃ isobtained per hour in the second solid-liquid separation device 92. 4.61m³ first ammonia water at 1.9 mass % concentration is obtained per hourin the second ammonia water storage tank 52, and the first ammonia watermay be reused in a zeolite production process.

Embodiment 7

As shown in FIG. 6, waste water containing ammonium salts (containing 63g/L NaCl, 65 g/L Na₂SO₄, 25.2 g/L NH₄Cl, 26.4 g/L (NH₄)₂SO₄, withpH=7.0) is fed at 5 m³/h feed rate into the pipeline of the treatmentsystem, 45.16 mass % sodium hydroxide solution is introduced into thepipeline for the first pH adjustment, the adjusted pH value is monitoredwith the first pH measuring device 61 (a pH meter) (the measured valueis 8.6), and then a part of the waste water is fed by means of the firstcirculation pump 71 into the first heat exchange device 31 to exchangeheat with the condensate of the second ammonia-containing vapor, and ismixed with the fifth mother liquid returned by the ninth circulationpump 79; the other part of the waste water is fed into the eleventh heatexchange device 30 to exchange heat with the third mother liquid; thetwo parts are merged to obtain waste water to be treated (wherein themolar ratio of SO₄ ²⁻ to Cl⁻ is 1:2.88); then the waste water to betreated is fed into the eighth heat exchange device 38 to exchange heatwith the second ammonia-containing vapor, so that the temperature of thewaste water to be treated is increased to 107° C.; next, sodiumhydroxide solution at 45.16 mass % concentration is introduced into thepipeline through which the waste water is fed into the second MVRevaporation device 3 for second pH adjustment, and the adjusted pH valueis monitored with the second pH measuring device 60 (a pH meter) (themeasured value is 10.8).

The second evaporation is executed in the second MVR evaporation device3 (falling film+forced circulation two-stage MVR evaporationcrystallizer), the evaporation temperature is 100° C., the pressure is−22.82 kPa, and the amount of evaporation is 4.00 m³/h; thus, secondammonia-containing vapor and second concentrated solution that containssodium sulfate crystal are obtained. The second ammonia-containing vaporis compressed in the first compressor 101 (the temperature is increasedby 16° C.), then the second ammonia-containing vapor flows through theeighth heat exchange device 38 and the first heat exchange device 31sequentially to exchange heat with the waste water to be treated and thewaste water containing ammonium salts respectively, so that firstammonia water is obtained, and stored in the first ammonia water storagetank 51. Besides, to improve the content of solids in the second MVRevaporation device 3, a part of the liquid after the evaporation in thesecond MVR evaporation device 3 is taken as circulating liquid andcirculated by means of the fifth circulation pump 75 to the eighth heatexchange device 38 for heat exchange, and then the circulating liquidenters into the second MVR evaporation device 3 again for secondevaporation (the second recirculation ratio is 80). The degree of thesecond evaporation is monitored with the densitometer provided on thesecond MVR evaporation device 3, to control the concentration of sodiumchloride in the second concentrated solution to be 273.9 g/L (4.682mol/L).

The second concentrated solution that contains sodium sulfate crystal,which is obtained in the evaporation in the second MVR evaporationdevice 3, is fed into the third solid-liquid separation device 93 (acentrifugal machine) for third solid-liquid separation; thus, 2.16 m³third mother liquid that contains 273.9 g/L NaCl, 61.9 g/L Na₂SO₄, 1.38g/L NaOH, and 0.34 g/L NH₃ is obtained per hour (the concentration ofCl⁻ is 4.682 mol/L, the concentration of SO₄ ²⁻ is 0.4359 mol/L), and isstored temporarily in the third mother liquid tank 50; the sodiumsulfate solid obtained in the solid-liquid separation (474.84 kg filtercake of sodium sulfate crystal with 1.5 mass % water content is obtainedper hour, wherein the content of sodium chloride is 1.5 mass % or lower)is eluted with 61 g/L sodium sulfate solution that is equal to the drymass of filter cake of sodium sulfate crystal, and is dried, so that467.71 kg sodium sulfate (at 99.4 mass % purity) is obtained per hour,and the washing liquid is circulated by means of the fourteenthcirculation pump 84 to the pipeline before the eighth heat exchangedevice 38 and mixed with the waste water containing ammonium salts; thenthe mixture is fed into the second MVR evaporation device 3 again forsecond evaporation.

After the third mother liquid is fed by means of the eleventhcirculation pump 70 into the eleventh heat exchange device 30 andexchanged heat with the waste water containing ammonium salts, the thirdmother liquid is further fed into the second heat exchange device 32 (aplastic heat exchanger) to exchange heat with the third mother liquid,so that the temperature of the third mother liquid is decreased to 15.8°C.; then, the third mother liquid is mixed with the circulating liquidtransferred by the second circulation pump 72 from the coolingcrystallization device 2, and exchanges heat with the refrigeratingliquid in the sixth heat exchange device 36 so that its temperature isfurther decreased; then, the third mother liquid is fed into the coolingcrystallization device 2 (a freezing crystallization tank) for coolingcrystallization, so that crystalline solution that contains sodiumsulfate crystal is obtained. Wherein the temperature of the coolingcrystallization is −2° C., and the time of the cooling crystallizationis 120 min., the recirculated amount in the cooling crystallization iscontrolled to be 98 m³/h, and the degree of super-saturation of sodiumsulfate in the cooling crystallization process is controlled so that itis not greater than 1.0 g/L.

The crystalline solution that contains sodium sulfate crystal, which isobtained in the cooling crystallization device 2, is fed into the firstsolid-liquid separation device 91 (a centrifugal machine) forsolid-liquid separation; thus, 1.98 m³ fourth mother liquid thatcontains 299.2 g/L NaCl, 15.6 g/L Na₂SO₄, 1.5 g/L NaOH, and 0.37 g/L NH₃is obtained per hour, and is stored temporarily in the first motherliquid tank 53; 228.49 kg filter cake of sodium sulfate decahydratecrystal at 98.2 mass % purity with 55 mass % water content is obtainedper hour, dissolved with the waste water containing ammonium salts, andthen fed by means of the first circulation pump 71 into the second MVRevaporation device 3 for second evaporation to prepare anhydrous sodiumsulfate.

The third evaporation process is executed in the first MVR evaporationdevice 1 (falling film+forced circulation two-stage MVR evaporatingcrystallizer). The fourth mother liquid is fed into the third heatexchange device 33 (a duplex stainless steel plate-type heat exchanger)to exchange heat with the condensate of the third ammonium-containingvapor, then is fed into the fourth heat exchange device 34 (a duplexstainless steel plate-type heat exchanger) to exchange heat with thecompressed third ammonium-containing vapor, and then is treated by thirdevaporation in the first MVR evaporation device 1 to obtain thirdconcentrated solution that contains sodium chloride crystal and thirdammonium-containing vapor. The temperature of the third evaporation is50° C., the pressure is −92.67 kPa, and the amount of evaporation is1.65 m³/h. After the third ammonium-containing vapor is compressed bythe second compressor 102 (the temperature is increased by 16° C.), itexchanges heat with the fourth mother liquid in the fourth heat exchangedevice 34 and the third heat exchange device 33 sequentially, so thatsecond ammonia water is obtained, and is stored in the second ammoniawater storage tank 52. In addition, to improve the solid content in thefirst MVR evaporation device 1, a part of the liquid after the thirdevaporation in the first MVR evaporation device 1 is circulated ascirculating liquid by means of the seventh circulation pump 77 to thefirst MVR evaporation device 1 again for third evaporation (the thirdrecirculation ratio is 87.5). The degree of the third evaporation ismonitored with the densitometer provided on the first MVR evaporationdevice 1, to control the concentration of sodium sulfate in the thirdconcentrated solution after third evaporation to be 0.970Y (65.3 g/L).

The third concentrated solution that contains sodium chloride crystal isfed into the second solid-liquid separation device 92 (a centrifugalmachine) for fifth solid-liquid separation, and then is eluted; thus,0.473 m³ fifth mother liquid that contains 293.6 g/L NaCl, 65.3 g/LNa₂SO₄, 6.3 g/L NaOH and 0.0016 g/L NH₃ is obtained per hour, and istemporarily stored in the second mother liquid tank 54; in addition, allof the fifth mother liquid is transferred by means of the ninthcirculation pump 79 to the waste water transport pipeline, and is mixedwith the waste water containing ammonium salts to obtain waste water tobe treated. The obtained solid sodium chloride (458.65 kg filter cake ofsodium chloride crystal with 1.4 mass % water content is obtained perhour, wherein the content of sodium sulfate is 1.5 mass % or lower) iseluted with 293 g/L sodium chloride solution in the same dry mass as thesodium chloride, and is dried in a drier, thus 452.23 kg sodium chloride(at 99.5 mass % purity) is obtained per hour; the fourth washing liquidobtained in the washing is returned by means of the tenth circulationpump 80 to the first MVR evaporation device 1.

In this embodiment, 4.00 m³ ammonia water at 1.7 mass % concentration isobtained per hour in the first ammonia water storage tank 51; 1.65 m³ammonia water at 0.04 mass % concentration is obtained per hour in thesecond ammonia water storage tank 52.

In addition, the tail gas discharged from the eighth heat exchangedevice 38, the cooling crystallization device 2, and the fourth heatexchange device 34 is introduced by means of the vacuum pump 81 into thetail gas absorption tower 83 for absorption. The tail gas absorptiontower 83 has circulating water in it, the circulating water iscirculated in the tail gas absorption tower 83 under the action of thefourth circulation pump 74, and water is replenished to the tail gasabsorption tower 83 by means of the third circulation pump 73 from thecirculating water tank 82 at the same time; in addition, fresh water isreplenished to the circulating water tank 82, and thereby thetemperature and ammonia content of the service water of the vacuum pump81 are decreased. Dilute sulfuric acid is further charged into the tailgas absorption tower 83 to absorb ammonia or the like in the tail gas.The MVR evaporation is initiated by charging steam at 143.3° C.temperature in the initial stage.

Embodiment 8

The waste water containing ammonium salts is treated with the methoddescribed in the embodiment 7, but: waste water containing ammoniumsalts that contains 45 g/L NaCl, 90 g/L Na₂SO₄, 15.1 g/L NH₄Cl and 30.7g/L (NH₄)₂SO₄ with pH=6.6 is treated, and the molar ratio of SO₄ ²⁻ toCl⁻ contained in the obtained waste water to be treated is 1:1.59, andthe temperature of the waste water to be treated is 102° C. after theheat exchange in the eighth heat exchange device 38.

The temperature of the second evaporation is 95° C., the pressure is−36.36 kPa, and the amount of evaporation is 4.51 m³/h; the temperatureof the cooling crystallization is −4° C., and the time is 120 min.; thetemperature of the third evaporation is 75° C., the pressure is −72.75kPa, and the amount of evaporation is 1.15 m³/h.

625.74 kg filter cake of sodium sulfate crystal with 1.4 mass % watercontent is obtained per hour in the third solid-liquid separation device93 (wherein the content of sodium chloride is 1.5 mass % or lower); thefilter cake of sodium sulfate crystal is eluted with 64 g/L sodiumsulfate solution that is in the same dry mass as the filter cake ofsodium sulfate crystal; after drying, 616.98 kg sodium sulfate (at 99.5mass % purity) is obtained per hour, and 1.56 m³ third mother liquidthat contains 267.3 g/L NaCl, 64.3 g/L Na₂SO₄, 1.83 g/L NaOH, and 0.41g/L NH₃ (the concentration of Cl⁻ is 4.569 mol/L, and the concentrationof SO₄ ²⁻ is 0.4528 mol/L) is obtained per hour.

181.65 kg filter cake of sodium sulfate decahydrate crystal with 56 mass% water content (at 98.1 mass % purity) is obtained per hour in thefirst solid-liquid separation device 91, dissolved with the waste watercontaining ammonium salts, and then returned to the second evaporation;1.41 m³ fourth mother liquid at concentrations of 295.1 g/L NaCl, 14.3g/L Na₂SO₄, 2.0 g/L NaOH, and 0.45 g/L NH₃ is obtained per hour.

310.34 kg filter cake of sodium chloride crystal with 1.5 mass % watercontent is obtained per hour in second solid-liquid separation device92, and finally 305.69 kg sodium chloride (at 99.6 mass % purity) isobtained per hour; 0.361 m³ fifth mother liquid at concentrations of300.9 g/L NaCl, 55.9 g/L Na₂SO₄, 7.89 g/L NaOH, and 0.0018 g/L NH₃ isobtained per hour in the second solid-liquid separation device 92.

4.51 m³ ammonia water at 1.3 mass % concentration is obtained per hourin the first ammonia water storage tank 51; 1.15 m³ ammonia water at0.05 mass % concentration is obtained per hour in the second ammoniawater storage tank 52.

Embodiment 9

The waste water containing ammonium salts is treated with the methoddescribed in the embodiment 7, but: waste water containing ammoniumsalts that contains 80 g/L NaCl, 42 g/L Na₂SO₄, 37.1 g/L NH₄Cl and 19.8g/L (NH₄)₂SO₄ with pH=6.9 is treated, and the molar ratio of SO₄ ²⁻ toCl⁻ contained in the obtained waste water to be treated is 1:6.03, andthe temperature of the waste water to be treated is 112° C. after theheat exchange in the eighth heat exchange device 38.

The temperature of the second evaporation is 105° C., the pressure is−7.01 kPa, and the amount of evaporation is 3.43 m³/h; the temperatureof the cooling crystallization is 0° C., and the time is 120 min.; thetemperature of the third evaporation is 100° C., the pressure is −22.83kPa, and the amount of evaporation is 2.11 m³/h.

319.54 kg filter cake of sodium sulfate crystal with 1.5 mass % watercontent is obtained per hour in the third solid-liquid separation device93 (wherein the content of sodium chloride is 1.5 mass % or lower); thefilter cake of sodium sulfate crystal is eluted with 59 g/L sodiumsulfate solution that is in the same dry mass as the filter cake ofsodium sulfate crystal; after drying, 314.75 kg sodium sulfate (at 99.6mass % purity) is obtained per hour, and 3.27 m³ third mother liquidthat contains 278.6 g/L NaCl, 59.2 g/L Na₂SO₄, 2.64 g/L NaOH, and 0.25g/L NH₃ (the concentration of Cl⁻ is 4.762 mol/L, and the concentrationof SO₄ ²⁻ is 0.4169 mol/L) is obtained per hour.

317.86 kg filter cake of sodium sulfate decahydrate crystal with 55 mass% water content (at 98.2 mass % purity) is obtained per hour in thefirst solid-liquid separation device 91; 3.02.m³ fourth mother liquid atconcentrations of 302 g/L NaCl, 16.8 g/L Na₂SO₄, 2.8 g/L NaOH, and 0.27g/L NH₃ is obtained per hour.

703.02 kg filter cake of sodium chloride crystal with 14 mass % watercontent is obtained per hour in second solid-liquid separation device92, and finally 604.60 kg sodium chloride (at 99.5 mass % purity) isobtained per hour; 1.02 m³ fifth mother liquid at concentrations of304.6 g/L NaCl, 50 g/L Na₂SO₄, 8.5 g/L NaOH, and 0.0008 g/L NH₃ isobtained per hour.

3.43 m³ ammonia water at 2.3 mass % concentration is obtained per hourin the first ammonia water storage tank 51; 2.1 m³ ammonia water at 0.04mass % concentration is obtained per hour in the second ammonia waterstorage tank 52.

Embodiment 10

As shown in FIG. 7, waste water containing ammonium salts (containing 58g/L NaCl, 66 g/L Na₂SO₄, 26.3 g/L NH₄Cl, 30.4 g/L (NH₄)₂SO₄, withpH=6.8) is fed at 5 m³/h feed rate into the pipeline of the treatmentsystem, 45.16 mass % sodium hydroxide solution is introduced into thepipeline for the first pH adjustment, the adjusted pH value is monitoredwith the first pH measuring device 61 (a pH meter) (the measured valueis 8.0), and then a part of the waste water containing ammonium salts isfed by means of the first circulation pump 71 into the first heatexchange device 31 to exchange heat with the condensate of the secondammonia-containing vapor, the other part of the waste water is mixedwith the third mother liquid returned by the ninth circulation pump 79and then is fed into the eleventh heat exchange device 30 to exchangeheat with the third mother liquid; the two parts are merged to obtainwaste water to be treated (wherein the molar ratio of SO₄ ²⁻ to Cl⁻ is1:2.42); then the waste water to be treated is fed into the eighth heatexchange device 38 to exchange heat with the second ammonia-containingvapor, so that the temperature of the waste water to be treated isincreased to 112° C.; next, sodium hydroxide solution at 45.16 mass %concentration is introduced into the pipeline through which the wastewater is fed into the second MVR evaporation device 3 for second pHadjustment, and the adjusted pH value is monitored with the second pHmeasuring device 60 (a pH meter) (the measured value is 10.8).

The second evaporation is executed in the second MVR evaporation device3 (falling film+forced circulation two-stage MVR evaporationcrystallizer), the evaporation temperature is 105° C., the pressure is−7.01 kPa, and the amount of evaporation is 4.12 m³/h; thus, secondammonia-containing vapor and second concentrated solution that containssodium sulfate crystal are obtained. The second ammonia-containing vaporis compressed in the first compressor 101 (the temperature is increasedby 16° C.), then the second ammonia-containing vapor flows through theeighth heat exchange device 38 and the first heat exchange device 31sequentially to exchange heat with the waste water to be treated and thewaste water containing ammonium salts, so that first ammonia water isobtained, and stored in the first ammonia water storage tank 51.Besides, to improve the content of solids in the second MVR evaporationdevice 3, a part of the liquid after the evaporation in the second MVRevaporation device 3 is taken as circulating liquid and circulated bymeans of the fifth circulation pump 75 to the eighth heat exchangedevice 38 for heat exchange, and then the circulating liquid enters intothe second MVR evaporation device 3 again for second evaporation (thesecond recirculation ratio is 82). The degree of the second evaporationis monitored with the densitometer provided on the second MVRevaporation device 3, to control the concentration of sodium chloride inthe second concentrated solution to be 273.5 g/L (4.675 mol/L).

The second concentrated solution that contains sodium sulfate crystal,which is obtained in the evaporation in the second MVR evaporationdevice 3, is fed into the third solid-liquid separation device 93 (acentrifugal machine) for third solid-liquid separation; thus, 1.90 m³third mother liquid that contains 273.5 g/L NaCl, 60.7 g/L Na₂SO₄, 1.67g/L NaOH, and 0.43 g/L NH₃ is obtained per hour (the concentration ofCl⁻ is 4.675 mol/L, the concentration of SO₄ ²⁻ is 0.4275 mol/L), and isstored temporarily in the third mother liquid tank 50; the sodiumsulfate solid obtained in the solid-liquid separation (500.52 kg filtercake of sodium sulfate crystal with 1.5 mass % water content is obtainedper hour, wherein the content of sodium chloride is 2.0 mass % or lower)is eluted with 60 g/L sodium sulfate solution that is equal to the drymass of filter cake of sodium sulfate crystal, and is dried, so that493.51 kg sodium sulfate (at 99.5 mass % purity) is obtained per hour,and the washing liquid is circulated by means of the fourteenthcirculation pump 84 to the pipeline before the eighth heat exchangedevice 38 and mixed with the waste water containing ammonium salts; thenthe mixture is fed into the second MVR evaporation device 3 again forsecond evaporation.

After the third mother liquid is fed by means of the eleventhcirculation pump 70 into the eleventh heat exchange device 30 andexchanged heat with the waste water containing ammonium salts, the thirdmother liquid is further fed into the second heat exchange device 32 (aplastic heat exchanger) to exchange heat with the third mother liquid,so that the temperature of the third mother liquid is decreased to 16°C.; then, the third mother liquid is mixed with the circulating liquidtransferred by the second circulation pump 72 from the coolingcrystallization device 2, and exchanges heat with the refrigeratingliquid in the sixth heat exchange device 36 so that its temperature isfurther decreased; then, the third mother liquid is fed into the coolingcrystallization device 2 (a continuous freezing crystallization tank)for cooling crystallization, so that crystalline solution that containssodium sulfate crystal is obtained. Wherein the temperature of thecooling crystallization is −2° C., and the time of the coolingcrystallization is 120 min., the recirculated amount in the coolingcrystallization is controlled to be 84 m³/h, and the degree ofsuper-saturation of sodium sulfate in the freezing process is controlledto be 1.0 g/L.

The crystalline solution that contains sodium sulfate crystal, which isobtained in the cooling crystallization device 2, is fed into the firstsolid-liquid separation device 91 (a centrifugal machine) forsolid-liquid separation; thus, 1.74 m³ second mother liquid thatcontains 299 g/L NaCl, 15.6 g/L Na₂SO₄, 1.8 g/L NaOH, and 0.46 g/L NH₃is obtained per hour, and is stored temporarily in the first motherliquid tank 53; 200.59 kg filter cake of sodium sulfate decahydratecrystal at 98 mass % purity with 56 mass % water content is obtained perhour, dissolved with the waste water containing ammonium salts, and thenfed by means of the first circulation pump 71 into the second MVRevaporation device 3 for second evaporation to prepare anhydrous sodiumsulfate.

The third evaporation process is executed in the first MVR evaporationdevice 1 (falling film+forced circulation two-stage MVR evaporatingcrystallizer). A part of the second mother liquid is fed into the thirdheat exchange device 33 (a duplex stainless steel plate-type heatexchanger) to exchange heat with the condensate of the thirdammonium-containing vapor after compression, the other part is fed intothe fifth heat exchange device 35 (a duplex stainless steel plate-typeheat exchanger) to exchange heat with the third concentrated solutionthat contains sodium chloride crystal obtained in the third evaporation,and then the two parts of second mother liquid are merged and loadedinto the fourth heat exchange device 34 (a duplex stainless steelplate-type heat exchanger) to exchange heat with the thirdammonium-containing vapor; next, the second mother liquid is treated bythird evaporation is executed in the first MVR evaporation device 1 toobtain third concentrated solution that contains sodium chloride crystaland third ammonium-containing vapor. The temperature of the thirdevaporation is 105° C., the pressure is −7.02 kPa, and the amount ofevaporation is 1.57 m³/h. After the third ammonium-containing vapor iscompressed by the second compressor 102 (the temperature is increased by16° C.), it exchanges heat with the second mother liquid in the fourthheat exchange device 34 and the third heat exchange device 33sequentially, so that second ammonia water is obtained, and is stored inthe second ammonia water storage tank 52. In addition, to improve thesolid content in the first MVR evaporation device 1, a part of theliquid after the third evaporation in the first MVR evaporation device 1is circulated as circulating liquid by means of the seventh circulationpump 77 to the first MVR evaporation device 1 again for thirdevaporation (the third recirculation ratio is 90). The degree of thethird evaporation is monitored with the mass flow meter provided on thefirst MVR evaporation device 1, to control the amount of evaporation inthe third evaporation to be 1.57 m³/h (equivalent to controlling theconcentration of sodium sulfate in the treated solution to be 0.978Y(87.4 g/L)).

The third concentrated solution that contains sodium sulfate crystal andsodium chloride crystal, which is obtained in the third evaporation, istreated by cooling treatment in the low temperature treatment tank 55(temperature: 20° C., time: 60 min.) to obtain treated solution thatcontains sodium chloride crystal. A stirring paddle is provided in thelow temperature treatment tank 55 and operates at 60 r/min. rotationspeed.

The treated solution that contains sodium chloride crystal, which isobtained in the cooling treatment, is fed into the second solid-liquidseparation device 92 (a centrifugal machine) for fifth solid-liquidseparation, and then is eluted; thus, 0.31 m³ third mother liquid thatcontains 277.5 g/L NaCl, 87.4 g/L Na₂SO₄, 10.2 g/L NaOH and 0.0026 g/LNH₃ is obtained per hour, and is temporarily stored in the second motherliquid tank 54; in addition, all of the third mother liquid istransferred by means of the ninth circulation pump 79 to the waste watertransport pipeline, and is mixed with the waste water containingammonium salts to obtain waste water to be treated. The obtained solidsodium chloride (440.53 kg filter cake of sodium chloride crystal with1.5 mass % water content is obtained per hour, wherein the content ofsodium sulfate is 1.5 mass % or lower) is eluted with 277 g/L sodiumchloride solution in the same dry mass as the sodium chloride, and isdried in a drier, thus 433.92 kg sodium chloride (at 99.5 mass % purity)is obtained per hour; the fourth washing liquid obtained in the washingis returned by means of the tenth circulation pump 80 to the first MVRevaporation device 1.

In this embodiment, 4.12 m³ ammonia water at 1.9 mass % concentration isobtained per hour in the first ammonia water storage tank 51; 1.57 m³ammonia water at 0.05 mass % concentration is obtained per hour in thesecond ammonia water storage tank 52.

In addition, the tail gas discharged from the eighth heat exchangedevice 38, the cooling crystallization device 2, and the fourth heatexchange device 34 is introduced by means of the vacuum pump 81 into thetail gas absorption tower 83 for absorption. The tail gas absorptiontower 83 has circulating water in it, the circulating water iscirculated in the tail gas absorption tower 83 under the action of thefourth circulation pump 74, water is replenished to the tail gasabsorption tower 83 by means of the third circulation pump 73 from thecirculating water tank 82 at the same time; in addition, fresh water isreplenished to the circulating water tank 82, and thereby thetemperature and ammonia content of the service water of the vacuum pump81 are decreased. Dilute sulfuric acid is further charged into the tailgas absorption tower 83 to absorb ammonia or the like in the tail gas.The MVR evaporation is initiated by charging steam at 143.3° C.temperature in the initial stage.

Embodiment 11

The waste water containing ammonium salts is treated with the methoddescribed in the embodiment 10, but: waste water containing ammoniumsalts that contains 46 g/L NaCl, 89 g/L Na₂SO₄, 15 g/L NH₄Cl and 29.5g/L (NH₄)₂SO₄ with pH=6.7 is treated, and the molar ratio of SO₄ ²⁻ toCl⁻ contained in the obtained waste water to be treated is 1:1.46, andthe temperature of the waste water to be treated is 102° C. after theheat exchange in the eighth heat exchange device 38.

The temperature of the second evaporation is 95° C., the pressure is−36.36 kPa, and the amount of evaporation is 4.51 m³/h; the temperatureof the cooling crystallization is −4° C., and the time is 120 min.; thetemperature of the third evaporation is 107° C., the pressure is 0 kPa,and the amount of evaporation is 0.54 m³/h; the temperature of thecooling treatment is 25° C., and the time is 58 min.

614.99 kg filter cake of sodium sulfate crystal with 1.5 mass % watercontent is obtained per hour in the third solid-liquid separation device93 (wherein the content of sodium chloride is 1.5 mass % or lower); thefilter cake of sodium sulfate crystal is eluted with 64 g/L sodiumsulfate solution that is in the same dry mass as the filter cake ofsodium sulfate crystal; after drying, 605.77 kg sodium sulfate (at 99.4mass % purity) is obtained per hour, and 1.39 m³ third mother liquidthat contains 268.7 g/L NaCl, 64.4 g/L Na₂SO₄, 1.15 g/L NaOH, and 0.44g/L NH₃ (the concentration of Cl⁺ is 4.593 mol/L, and the concentrationof SO₄ ²⁻ is 0.4535 mol/L) is obtained per hour.

158.68 kg filter cake of sodium sulfate decahydrate crystal with 55 mass% water content (at 98.3 mass % purity) is obtained per hour in thefirst solid-liquid separation device 91, dissolved with the waste watercontaining ammonium salts, and then returned to the second evaporation;1.27 m³ second mother liquid at concentrations of 295.5 g/L NaCl, 14.4g/L Na₂SO₄, 1.26 g/L NaOH, and 0.48 g/L NH₃ is obtained per hour.

314.32 kg filter cake of sodium chloride crystal with 1.4 mass % watercontent is obtained per hour in second solid-liquid separation device92, and finally 309.92 kg sodium chloride (at 99.5 mass % purity) isobtained per hour; 0.222 m³ third mother liquid at concentrations of279.5 g/L NaCl, 82.2 g/L Na₂SO₄, 7.2 g/L NaOH, and 0.0028 g/L NH₃ isobtained per hour.

4.51 m³ ammonia water at 1.3 mass % concentration is obtained per hourin the first ammonia water storage tank 51; 1.14 m³ ammonia water at0.05 mass % concentration is obtained per hour in the second ammoniawater storage tank 52.

Embodiment 12

The waste water containing ammonium salts is treated with the methoddescribed in the embodiment 10, but: waste water containing ammoniumsalts that contains 82 g/L NaCl, 42 g/L Na₂SO₄, 36.5 g/L NH₄Cl and 19g/L (NH₄)₂SO₄ with pH=6.2 is treated, and the molar ratio of SO₄ ²⁻ toCl⁻ contained in the obtained waste water to be treated is 1:5.20, andthe temperature of the waste water to be treated is 107° C. after theheat exchange in the eighth heat exchange device 38.

The temperature of the second evaporation is 100° C., the pressure is−22.82 kPa, and the amount of evaporation is 3.47 m³/h; the temperatureof the cooling crystallization is 0° C., and the time is 120 min.; thetemperature of the third evaporation is 105° C., the pressure is −7.02kPa, and the amount of evaporation is 2.16 m³/h; the temperature of thecooling treatment is 30° C., and the time is 55 min.

315.15 kg filter cake of sodium sulfate crystal with 1.4 mass % watercontent is obtained per hour in the third solid-liquid separation device93 (wherein the content of sodium chloride is 1.5 mass % or lower); thefilter cake of sodium sulfate crystal is eluted with 60 g/L sodiumsulfate solution that is in the same dry mass as the filter cake ofsodium sulfate crystal; after drying, 310.74 kg sodium sulfate (at 99.5mass % purity) is obtained per hour, and 2.71 m³ third mother liquidthat contains 279.1 g/L NaCl, 60.3 g/L Na₂SO₄, 2.2 g/L NaOH, and 0.30g/L NH₃ (the concentration of Cl⁻ is 4.771 mol/L, and the concentrationof SO₄ ²⁻ is 0.4246 mol/L) is obtained per hour.

278.01 kg filter cake of sodium sulfate decahydrate crystal with 56 mass% water content (at 98.6 mass % purity) is obtained per hour in thefirst solid-liquid separation device 91, dissolved with the waste watercontaining ammonium salts, and then returned to the second evaporation;2.49 m³ second mother liquid at concentrations of 304.3 g/L NaCl, 16.8g/L Na₂SO₄, 2.39 g/L NaOH, and 0.33 g/L NH₃ is obtained per hour.

620.36 kg filter cake of sodium chloride crystal with 1.5 mass % watercontent is obtained per hour in second solid-liquid separation device92, and finally 611.05 kg sodium chloride (at 99.5 mass % purity) isobtained per hour; 0.527 m³ third mother liquid at concentrations of 281g/L NaCl, 78.5 g/L Na₂SO₄, 11.3 g/L NaOH, and 0.0016 g/L NH₃ is obtainedper hour.

3.47 m³ ammonia water at 2.2 mass % concentration is obtained per hourin the first ammonia water storage tank 51; 2.16 m³ ammonia water at0.038 mass % concentration is obtained per hour in the second ammoniawater storage tank 52.

Embodiment 13

As shown in FIG. 8, waste water containing ammonium salts (containing130 g/L NaCl, 26 g/L Na₂SO₄, 40 g/L NH₄Cl, 8.1 g/L (NH₄)₂SO₄, withpH=6.5) is fed at 5.859 m³/h feed rate into the pipeline of thetreatment system, sodium hydroxide solution at 45.16 mass %concentration is introduced into the pipeline for first pH adjustment,and the adjusted pH value is monitored with the first pH measuringdevice 61 (a pH meter) (the measured value is 9.0); a part of the wastewater containing ammonium salts is fed at 5.0 m³/h feed rate by means ofthe first circulation pump 71 and mixed with the seventh mother liquidreturned by the ninth circulation pump 79 to obtain waste water to betreated (wherein the concentration of Cl⁻ is 3.737 mol/L, theconcentration of SO₄ ²⁻ is 0.197 mol/L, and the molar ratio of Cl⁻/SO₄²⁻ is 18.97); then a part of the waste water to be treated is fed intothe first heat exchange device 31 to exchange heat with the condensateof the fourth ammonia-containing vapor, so that the temperature of thewaste water is increased to 102° C.; at the same time, the remainingpart of the waste water to be treated is fed into the fifth heatexchange device 35 to exchange heat with the fourth concentratedsolution that contains sodium chloride crystal, which is obtained byevaporation, so that the temperature of the waste water is increased to103° C.; next, the two parts of waste water to be treated is merged andfed into the second heat exchange device 32; the waste water to betreated is fed into the pipeline of the second heat exchange device 32,sodium hydroxide solution at 45.16 mass % concentration is introducedinto the pipeline for second pH adjustment, and the adjusted pH value ismonitored with the second pH measuring device 62 (a pH meter) (themeasured value is 11); next, the waste water to be treated is fed intothe second heat exchange device 32 to exchange heat with the fourthammonia-containing vapor, so that the temperature of the waste water tobe treated is increased to 112° C.; finally, the waste water to betreated is fed into the first MVR evaporation device 1 (a fallingfilm+forced circulation two-stage MVR evaporating crystallizer) forfourth evaporation; thus, fourth ammonia-containing vapor and fourthconcentrated solution that contains sodium chloride crystal and sodiumsulfate crystal are obtained, the evaporation temperature is 105° C.,the pressure is −7.02 kPa, and the amount of evaporation is 6.116 m³/h.After the fourth ammonium-containing vapor is compressed by thecompressor 101 (the temperature is increased by 19° C.), it exchangesheat with the waste water to be treated in the second heat exchangedevice 32 and the first heat exchange device 31 sequentially, so thatammonia water is obtained, and is stored in the first ammonia waterstorage tank 51. In addition, to improve the solid content in the firstMVR evaporation device 1, a part of the liquid after the evaporation inthe first MVR evaporation device 1 is circulated as circulating liquidby means of the seventh circulation pump 77 to the first MVR evaporationdevice 1 again for evaporation (the recirculation ratio is 120). Thedegree of the evaporation is monitored with the mass flow meter providedon the first MVR evaporation device 1, to control the amount ofevaporation in the evaporation to 6.012 m³/h (equivalent to controllingthe concentration of sodium sulfate in the treated solution to 0.9787Y(91.7 g/L)).

After the fourth concentrated solution that contains sodium chloridecrystal and sodium sulfate crystal exchanges heat with a part of thewaste water to be treated in the fifth heat exchange device 35, it isfed into the low temperature treatment tank 22 for cooling treatment(temperature: 17.9° C., time: 70 min.), to obtain treated solution thatcontains sodium chloride crystal. A stirring paddle is provided in thelow temperature treatment tank 22 and operates at 60 r/min. rotationspeed.

The treated solution that contains sodium chloride crystal is fed intothe first solid-liquid separation device 91 (a centrifugal machine) forsolid-liquid separation, and then is eluted; thus, 2.606 m³ sixth motherliquid that contains 277.7 g/L NaCl, 91.7 g/L Na₂SO₄, 2.2 g/L NaOH and0.66 g/L NH₃ is obtained per hour, and is temporarily stored in thefirst mother liquid tank 53. The obtained solid sodium chloride (1,202.7kg filter cake of sodium chloride crystal with 15 mass % water contentis obtained per hour, wherein the content of sodium sulfate is 3.1 mass% or lower) is eluted with 277.7 g/L sodium chloride solution in thesame dry mass as the sodium chloride, and is dried in a drier, thus1,022.3 kg sodium chloride (at 99.3 mass % purity) is obtained per hour;the seventh washing liquid obtained in the washing is returned by meansof the eighth circulation pump 78 to the fifth heat exchange device 35.

The other part of waste water containing ammonium salts is fed at 0.859m³/h feed rate and mixed with the sixth mother liquid in the firstmother liquid tank 53 (wherein the concentration of NaCl is 241 g/L, andthe concentration of Na₂SO₄ is 69 g/L); the sixth mother liquidexchanges heat with the seventh mother liquid in the third heat exchangedevice 33 via the sixth circulation pump 76, so that the temperature ofthe sixth mother liquid is decreased to 2.1° C.; then the sixth motherliquid is mixed with sodium sulfate crystal eluent and cooledcirculating liquid, and the resultant mixture further exchanges heatwith the refrigerating liquid in the sixth heat exchange device 36; thenthe mixture is fed into the cooling crystallization device 2 (acontinuous cooling crystallization tank) for cooling crystallization, sothat crystalline solution that contains sodium sulfate crystal isobtained. Wherein the temperature of the cooling crystallization is −2°C., and the time of the cooling crystallization is 130 min., therecirculated amount in the cooling crystallization is controlled to be181 m³/h, and the degree of super-saturation of sodium sulfate in thecooling crystallization process is controlled so that it is not greaterthan 1.0 g/L.

The crystalline solution that contains sodium sulfate crystal, which isobtained in the cooling crystallization device 2, is fed into the secondsolid-liquid separation device 92 (a centrifugal machine) and treated bysolid-liquid separation and elution; thus, 2.793 m³ sixth mother liquidthat contains 299 g/L NaCl, 15.8 g/L Na₂SO₄, and 5.08 g/L NH₃ isobtained per hour, stored temporarily in the second mother liquid tank54, and then returned to mix with the waste water containing ammoniumsalts to obtain waste water to be treated; the obtained sodium sulfatedecahydrate crystal (wherein the content of sodium chloride is 3.0 mass% or lower) is eluted with 15.8 g/L sodium sulfate solution that is inthe same dry mass as the sodium sulfate; so that 797.2 kg filter cake ofsodium sulfate decahydrate crystal with 75 mass % water content at 98.6mass % purity is obtained per hour.

In this embodiment, 6.012 m³ ammonia water at 1.39 mass % concentrationis obtained per hour in the first ammonia water storage tank 51.

In addition, the tail gas discharged from the cooling crystallizationdevice 2 and the second heat exchange device 32 is introduced by meansof the vacuum pump 81 into the tail gas absorption tower 83 forabsorption. The tail gas absorption tower 83 has circulating water init, the circulating water is circulated in the tail gas absorption tower83 under the action of the fourth circulation pump 74, and water isreplenished to the tail gas absorption tower 83 by means of the thirdcirculation pump 73 from the circulating water tank 82 at the same time;in addition, fresh water is replenished to the circulating water tank82, and thereby the temperature and ammonia content of the service waterof the vacuum pump 81 are decreased. Dilute sulfuric acid is furthercharged into the tail gas absorption tower 83 to absorb ammonia or thelike in the tail gas. The MVR evaporation is initiated by charging steamat 143.3° C. temperature in the initial stage.

Embodiment 14

The waste water containing ammonium salts is treated with the methoddescribed in the embodiment 13, but: waste water containing ammoniumsalts that contains 68 g/L NaCl, 68 g/L Na₂SO₄, 25 g/L NH₄Cl, and 25.4g/L (NH₄)₂SO₄ with pH=6.3 is treated, at 6.84 m³/h feed rate; a part ofthe waste water is fed at 5.0 m³/h feed rate and mixed with the seventhmother liquid returned by the ninth circulation pump 79 to obtain wastewater to be treated, in which the molar ratio of Cl⁻ to SO₄ ²⁻ is10.848; the remaining part of waste water containing ammonium salts ismixed with the sixth mother liquid in the first mother liquid tank 53 toobtain waste water to be treated, in which the concentration of NaCl is237.85 g/L, and the concentration of Na₂SO₄ is 71.39 g/L.

The evaporation temperature is 100° C., the pressure is −22.83 kPa, andthe amount of evaporation is 5.530 m³/h. The temperature of the coolingtreatment is 20° C., and the time is 65 min. The temperature of thecooling crystallization is 0° C., and the time is 120 min.

755.64 kg filter cake of sodium chloride crystal with 14.5 mass % watercontent is obtained per hour in the first solid-liquid separation device91, and finally 646.08 kg sodium chloride (at 99.2 mass % purity) isobtained per hour; 7.433 m³ sixth mother liquid at concentrations of279.9 g/L NaCl, 88.9 g/L Na₂SO₄, 2.2 g/L NaOH, and 0.27 g/L NH₃ isobtained per hour.

2,531.56 kg filter cake of sodium sulfate decahydrate crystal with 74mass % water content (at 98.3 mass % purity) is obtained per hour in thesecond solid-liquid separation device 92; 7.265 m³ first mother liquidat concentrations of 303.9 g/L NaCl, 17 g/L Na₂SO₄, and 3.86 g/L NH₃ isobtained per hour.

5.530 m³ ammonia water at 1.7 mass % concentration is obtained per hourin the first ammonia water storage tank 51, and the ammonia water may bereused in a zeolite production process.

Embodiment 15

The waste water containing ammonium salts is treated with the methoddescribed in the embodiment 13, but: waste water containing ammoniumsalts that contains 50 g/L NaCl, 100 g/L Na₂SO₄, 21 g/L NH₄Cl, and 42.69g/L (NH₄)₂SO₄ with pH=6.7 is treated, at 9.39 m³/h feed rate; a part ofthe waste water is fed at 5.0 m³/h feed rate and mixed with the seventhmother liquid returned by the ninth circulation pump 79 to obtain wastewater to be treated, in which the molar ratio of Cl⁻ to SO₄ ²⁻ is11.640; the remaining part of waste water containing ammonium salts ismixed with the sixth mother liquid in the first mother liquid tank 53 toobtain waste water to be treated, in which the concentration of NaCl is224.49 g/L, and the concentration of Na₂SO₄ is 62.84 g/L. After the heatexchange in the second heat exchange device 32, the temperature of thewaste water to be treated is 105° C.

The evaporation temperature is 110° C., the pressure is 11.34 kPa, andthe amount of evaporation is 5.999 m³/h. The temperature of the coolingtreatment is 25° C., and the time is 60 min. The temperature of thecooling crystallization is −4° C., and the time is 120 min.

775.47 kg filter cake of sodium chloride crystal with 14 mass % watercontent is obtained per hour in the first solid-liquid separation device91, and finally 666.90 kg sodium chloride (at 99.4 mass % purity) isobtained per hour; 13.876 m³ sixth mother liquid at concentrations of279.7 g/L NaCl, 82.4 g/L Na₂SO₄, 2.2 g/L NaOH, and 0.23 g/L NH₃ isobtained per hour.

5,445.10 kg filter cake of sodium sulfate decahydrate crystal with 74.5mass % water content (at 98.4 mass % purity) is obtained per hour in thesecond solid-liquid separation device 92; 13.900 m³ seventh motherliquid at concentrations of 295 g/L NaCl, 14.5 g/L Na₂SO₄, and 5.70 g/LNH₃ is obtained per hour.

5.999 m³ ammonia water at 2.6 mass % concentration is obtained per hourin the first ammonia water storage tank 51, and the ammonia water may bereused in a zeolite production process.

Embodiment 16

As shown in FIG. 9, waste water containing ammonium salts (containing120 g/L NaCl, 48 g/L Na₂SO₄, 23 g/L NH₄Cl, 9.35 g/L (NH₄)₂SO₄, withpH=6.8) is fed at 8.40 m³/h feed rate into the pipeline of the treatmentsystem, sodium hydroxide solution at 45.16 mass % concentration isintroduced into the pipeline for first pH adjustment, and the adjustedpH value is monitored with the first pH measuring device 61 (a pH meter)(the measured value is 9.1); then 3.40 m³/h waste water containingammonium salts is fed by means of the first circulation pump 71 into thefirst mother liquid tank 53 to mix with the sixth mother liquid, anotherpart of waste water containing ammonium salts is fed into the first heatexchange device 31 to exchange heat with the condensate of the fourthammonia-containing vapor, the remaining part of the waste watercontaining ammonium salts is mixed with the seventh mother liquidreturned by the ninth circulation pump 79, and then is fed into thefifth heat exchange device 35 to exchange heat with the sixth motherliquid; next, the parts of waste water that have exchanged heat in thefirst heat exchange device 31 and the fifth heat exchange device 35 aremerged to obtain waste water to be treated, wherein the temperature ofthe waste water to be treated is 80° C., the concentration of Cl⁻ is4.284 mol/L, the concentration of SO₄ ²⁻ is 0.1945 mol/L, and the molarratio of Cl⁻/SO₄ ²⁻ is 22.025; the waste water to be treated is fed intothe pipeline of the second heat exchange device 32, sodium hydroxidesolution at 45.16 mass % concentration is introduced into the pipelinefor second pH adjustment, and the adjusted pH value is monitored withthe second pH measuring device 62 (a pH meter) (the measured value is11); next, the waste water to be treated is fed into the second heatexchange device 32 to exchange heat with the fourth ammonia-containingvapor, so that the temperature of the waste water to be treated isincreased to 107° C.; finally, the waste water to be treated is fed intothe first MVR evaporation device 1 (a falling film+forced circulationtwo-stage MVR evaporating crystallizer) for evaporation; thus, fourthammonia-containing vapor and fourth concentrated solution that containssodium chloride crystal and sodium sulfate crystal are obtained, theevaporation temperature is 100° C., the pressure is −22.83 kPa, and theamount of evaporation is 7.71 m³/h. After the fourth ammonium-containingvapor is compressed by the compressor 101 (the temperature is increasedby 17° C.), it exchanges heat with the waste water to be treated and thewaste water containing ammonium salts in the second heat exchange device32 and the first heat exchange device 31 sequentially, so that ammoniawater is obtained, and is stored in the first ammonia water storage tank51. In addition, to improve the solid content in the first MVRevaporation device 1, a part of the liquid after the evaporation in thefirst MVR evaporation device 1 is circulated as circulating liquid bymeans of the seventh circulation pump 77 to the first MVR evaporationdevice 1 again for evaporation (the recirculation ratio is 154). Thedegree of the evaporation is monitored with the densitometer provided onthe first MVR evaporation device 1, to control the concentration ofsodium sulfate in the fourth concentrated solution after evaporation tobe 0.9625Y (51.3 g/L).

The fourth concentrated solution that contains sodium chloride crystalis fed into the first solid-liquid separation device 91 (a centrifugalmachine) for solid-liquid separation, and then is eluted; thus, 9.81 m³sixth mother liquid that contains 308.6 g/L NaCl, 51.3 g/L Na₂SO₄, 2.2g/L NaOH and 0.17 g/L NH₃ is obtained per hour, and is temporarilystored in the first mother liquid tank 53. After the obtained solidsodium chloride (the content of sodium sulfate is 3.2 mass % or lower)is eluted with 308.6 g/L sodium chloride solution in the same dry massas the sodium chloride, a part of the filter cake of sodium chloridecrystal is used to prepare 308.6 g/L sodium chloride solution; 1,419.17kg filter cake of sodium chloride crystal with 14 mass % water contentis obtained per hour and dried in a drier; thus, 1,220.49 kg sodiumchloride (at 99.5 mass % purity) is obtained per hour, and the washingliquid obtained in the washing is circulated by means of the eighthcirculation pump 78 to a position before the second pH adjustment.

As described above, 3.40 m³/h waste water containing ammonium salts ismixed with the sixth mother liquid in the first mother liquid tank 53(the measured concentration of NaCl is 260 g/L, and the measuredconcentration of Na₂SO₄ is 38.2 g/L), the sixth mother liquid is fed bythe sixth circulation pump 76 and exchanges heat with the mixed solutionof waste water containing ammonium salts and the seventh mother liquidin the fifth heat exchange device 35, and then exchanges heat with theseventh mother liquid in the third heat exchange device 33 so that thetemperature of the sixth mother liquid is decreased to 0° C.; next, thesixth mother liquid is mixed with sodium sulfate crystal eluent andcooled circulating liquid, and the resultant mixture further exchangesheat with the refrigerating liquid in the sixth heat exchange device 36,and then is fed into the cooling crystallization device 2 (a consecutivefreezing crystallization tank) for cooling crystallization, to obtaincrystalline solution that contains sodium sulfate crystal. Wherein thetemperature of the cooling crystallization is −4° C., and the time ofthe cooling crystallization is 125 min., the recirculated amount in thecooling crystallization is controlled to be 300 m³/h, and the degree ofsuper-saturation of sodium sulfate in the cooling crystallizationprocess is controlled so that it is not greater than 1.0 g/L.

The crystalline solution that contains sodium sulfate crystal, which isobtained in the cooling crystallization device 2, is fed into the secondsolid-liquid separation device 92 (a centrifugal machine) forsolid-liquid separation, and then is eluted; thus, 11.60 m³ sixth motherliquid that contains 296 g/L NaCl, 14.5 g/L Na₂SO₄, and 2.93 g/L NH₃ isobtained per hour, and is stored temporarily in the second mother liquidtank 54; after the obtained sodium sulfate crystal (the content ofsodium chloride is 3.1 mass % or lower) is eluted with 14.5 g/L sodiumsulfate solution that is in the same dry mass as the sodium sulfate,1,946.10 kg filter cake of sodium sulfate decahydrate crystal at 99.0mass % purity with 75 mass % water content is obtained per hour.

In this embodiment, 7.71 m³ ammonia water at 1.0 mass % concentration isobtained per hour in the first ammonia water storage tank 51.

In addition, the tail gas discharged from the cooling crystallizationdevice 2 and the second heat exchange device 32 is introduced by meansof the vacuum pump 81 into the tail gas absorption tower 83 forabsorption. The tail gas absorption tower 83 has circulating water init, the circulating water is circulated in the tail gas absorption tower83 under the action of the fourth circulation pump 74, and water isreplenished to the tail gas absorption tower 83 by means of the thirdcirculation pump 73 from the circulating water tank 82 at the same time;in addition, fresh water is replenished to the circulating water tank82, and thereby the temperature and ammonia content of the service waterof the vacuum pump 81 are decreased. Dilute sulfuric acid is furthercharged into the tail gas absorption tower 83 to absorb ammonia or thelike in the tail gas. The MVR evaporation is initiated by charging steamat 143.3° C. temperature in the initial stage.

Embodiment 17

The waste water containing ammonium salts is treated with the methoddescribed in the embodiment 16, but: waste water containing ammoniumsalts that contains 68 g/L NaCl, 100 g/L Na₂SO₄, 24 g/L NH₄Cl, and 35.9g/L (NH₄)₂SO₄ with pH=6.7 is treated, at 13.3 m³/h feed rate; 5.0 m³/hwaste water containing ammonium salts is mixed with the seventh motherliquid returned by the ninth circulation pump 79 to obtain waste waterto be treated, in which the molar ratio of Cl⁻ to SO₄ ²⁻ is 18.948; theremaining part of waste water containing ammonium salts is mixed withthe sixth mother liquid in the first mother liquid tank 53 to obtainmixed solution, in which the concentration of NaCl is 247.0 g/L, and theconcentration of Na₂SO₄ is 43.6 g/L.

The evaporation temperature is 75° C., the pressure is −72.75 kPa, andthe amount of evaporation is 8.9 m³/h. The temperature of the coolingcrystallization is −2° C., and the time is 120 min.

1,462.30 kg filter cake of sodium chloride crystal with 15 mass % watercontent is obtained per hour in the first solid-liquid separation device91, and finally 1,242.96 kg sodium chloride (at 99.5 mass % purity) isobtained per hour; 25.58 m³ sixth mother liquid at concentrations of305.1 g/L NaCl, 57.5 g/L Na₂SO₄, 0.80 g/L NaOH, and 0.35 g/L NH₃ isobtained per hour.

7269.86 kg filter cake of sodium sulfate decahydrate crystal with 74.5mass % water content (at 99.1 mass % purity) is obtained per hour in thesecond solid-liquid separation device 92; 28.02 m³ seventh mother liquidat concentrations of 298.9 g/L NaCl, 15.7 g/L Na₂SO₄, and 5.11 g/L NH₃is obtained per hour.

8.90 m³ ammonia water at 2.3 mass % concentration is obtained per hourin the first ammonia water storage tank 51, and the ammonia water may bereused in a zeolite production process.

Embodiment 18

The waste water containing ammonium salts is treated with the methoddescribed in the embodiment 16, but: waste water containing ammoniumsalts that contains 99 g/L NaCl, 101 g/L Na₂SO₄, 26 g/L NH₄Cl, and 27g/L (NH₄)₂SO₄ with pH=6.9 is treated, at 12.15 m³/h feed rate; 5.0 m³/hwaste water containing ammonium salts is mixed with the seventh motherliquid returned by the ninth circulation pump 79 to obtain waste waterto be treated, in which the molar ratio of Cl⁻ to SO₄ ²⁻ is 16.938; theremaining part of waste water containing ammonium salts is mixed withthe sixth mother liquid in the first mother liquid tank 53 to obtainmixed solution, in which the concentration of NaCl is 238.5 g/L, and theconcentration of Na₂SO₄ is 47.1 g/L.

The evaporation temperature is 50° C., the pressure is −92.67 kPa, andthe amount of evaporation is 8.76 m³/h; the temperature of the coolingcrystallization is −4° C., and the time is 120 min.

1,788.93 kg filter cake of sodium chloride crystal with 14 mass % watercontent is obtained per hour in the first solid-liquid separation device91, and finally 1,538.48 kg sodium chloride (at 99.5 mass % purity) isobtained per hour; 17.77 m³ sixth mother liquid at concentrations of294.6 g/L NaCl, 65.7 g/L Na₂SO₄, 0.22 g/L NaOH, and 0.23 g/L NH₃ isobtained per hour.

6,113.15 kg filter cake of sodium sulfate decahydrate crystal with 74mass % water content (at 98.9 mass % purity) is obtained per hour in thesecond solid-liquid separation device 92; 20.05 m³ seventh mother liquidat concentrations of 296.3 g/L NaCl, 14.6 g/L Na₂SO₄, and 5.6 g/L NH₃ isobtained per hour.

8.76 m³ ammonia water at 1.9 mass % concentration is obtained per hourin the first ammonia water storage tank 51, and the ammonia water may bereused in a zeolite production process.

While some preferred embodiments of the present invention are describedabove, the present invention is not limited in those embodiments. Thoseskilled in the art can make modifications and variations to thetechnical scheme of the present invention, including combination oftechnical features in any appropriate form, all these variations andcombinations shall be deemed as the disclosure of the present invention,and fall into the scope of the present invention.

1. A waste water treatment apparatus for treating waste water containingammonium salts, comprising: a cooling crystallization unit, a firstsolid-liquid separation unit, a pH adjustment unit, a first evaporationunit, and a second solid-liquid separation unit, which are connectedsequentially, wherein the cooling crystallization unit is configured totreat the waste water by cooling crystallization, to obtaincrystal-containing crystalline solution; the first solid-liquidseparation unit is configured to treat the crystal-containingcrystalline solution by first solid-liquid separation; the pH adjustmentunit is configured to adjust the pH value of the liquid phase obtainedin the first solid-liquid separation before evaporation is executed; thefirst evaporation unit is configured to treat the liquid phase obtainedin the first solid-liquid separation unit by first evaporation, toobtain first ammonia-containing vapor and first crystal-containingconcentrated solution; the second solid-liquid separation unit isconfigured to treat the first crystal-containing concentrated solutionby second solid-liquid separation.
 2. The waste water treatmentapparatus according to claim 1, further comprising a low-temperaturetreatment unit arranged between the first evaporation unit and thesecond solid-liquid separation unit, the low-temperature treatment unitis configured to treat the concentrated solution obtained in the firstevaporation unit by low temperature treatment, to obtain treatedsolution; preferably, further comprising a pipeline configured to returnthe liquid phase obtained in the second solid-liquid separation unit tothe cooling crystallization unit.
 3. The waste water treatment apparatusaccording to claim 1, wherein the first evaporation unit is selectedfrom one or more of MVR evaporation device, single-effect evaporationdevice, multi-effect evaporation device, and flash evaporation devicerespectively; preferably, the cooling crystallization unit is a freezingcrystallization tank; preferably, the first solid-liquid separation unitand the second solid-liquid separation unit are selected from one ormore of centrifugation device, filtering device, and sedimentationdevice respectively. preferably, the pH adjustment unit is a pH adjustorintroduction device.
 4. A waste water treatment apparatus for treatingwaste water containing ammonium salts, comprising: a pH adjustment unit,a second evaporation unit, a third solid-liquid separation unit, acooling crystallization unit, a first solid-liquid separation unit, afirst evaporation unit, and a second solid-liquid separation unit, whichare connected sequentially, the pH adjustment unit is configured toadjust the pH of the waste water before evaporation is executed; thesecond evaporation unit is configured to treat the waste water by secondevaporation, to obtain second ammonia-containing vapor and secondcrystal-containing concentrated solution; the third solid-liquidseparation unit is configured to treat the second crystal-containingconcentrated solution by third solid-liquid separation; the coolingcrystallization unit is configured to treat the liquid phase obtained inthe third solid-liquid separation by cooling crystallization, to obtaincrystal-containing crystalline solution; the first solid-liquidseparation unit is configured to treat the crystal-containingcrystalline solution by first solid-liquid separation; the firstevaporation unit is configured to treat the liquid phase obtained in thefirst solid-liquid separation unit by first evaporation, to obtain firstammonia-containing vapor and first crystal-containing concentratedsolution; the second solid-liquid separation unit is configured to treatthe first crystal-containing concentrated solution by secondsolid-liquid separation; preferably, the waste water treatment apparatusfurther comprises a pipeline configured to return the liquid phaseobtained in the second solid-liquid separation unit to the secondevaporation unit.
 5. The waste water treatment apparatus according toclaim 4, further comprising a low-temperature treatment unit arrangedbetween the first evaporation unit and the second solid-liquidseparation unit, the low-temperature treatment unit is configured totreat the concentrated solution obtained in the first evaporation unitby low temperature treatment, to obtain treated solution; preferably,wherein the first evaporation unit and the second evaporation unit areselected from one or more of MVR evaporation device, single-effectevaporation device, multi-effect evaporation device, and flashevaporation device respectively; preferably, the cooling crystallizationunit is a freezing crystallization tank; preferably, the firstsolid-liquid separation unit, the second solid-liquid separation unit,and the third solid-liquid separation unit are selected from one or moreof centrifugation device, filtering device, and sedimentation devicerespectively. preferably, the pH adjustment unit is a pH adjustorintroduction device.
 6. A waste water treatment apparatus for treatingwaste water containing ammonium salts, comprising: a pH adjustment unit,a first evaporation unit, a first solid-liquid separation unit, acooling crystallization unit, and a second solid-liquid separation unit,which are connected sequentially, wherein the pH adjustment unit isconfigured to adjust the pH of the waste water before evaporation isexecuted; the first evaporation unit is configured to treat the wastewater by first evaporation, to obtain first ammonia-containing vapor andfirst crystal-containing concentrated solution; the first solid-liquidseparation unit is configured to treat the first crystal-containingconcentrated solution by first solid-liquid separation; the coolingcrystallization unit is configured to treat the liquid phase obtained inthe first solid-liquid separation unit by cooling crystallization, toobtain crystal-containing crystalline solution; the second solid-liquidseparation unit is configured to treat the crystal-containingcrystalline solution by second solid-liquid separation.
 7. The wastewater treatment apparatus according to claim 6, further comprising alow-temperature treatment unit arranged between the first evaporationunit and the first solid-liquid separation unit, the low-temperaturetreatment unit is configured to treat the concentrated solution obtainedin the first evaporation unit by low temperature treatment, to obtaintreated solution; preferably, further comprising a pipeline configuredto return the liquid phase obtained in the second solid-liquidseparation unit to the first evaporation unit.
 8. The waste watertreatment apparatus according to claim 6, wherein the first evaporationunit is selected from one or more of MVR evaporation device,single-effect evaporation device, multi-effect evaporation device, andflash evaporation device respectively; preferably, the coolingcrystallization unit is a freezing crystallization tank; preferably, thefirst solid-liquid separation unit and the second solid-liquidseparation unit are selected from one or more of centrifugation device,filtering device, and sedimentation device respectively; preferably, thepH adjustment unit is a pH adjustor introduction device.
 9. A method fortreating waste water containing ammonium salts that contains NH₄ ⁺, SO₄²⁻, Cl⁻ and Na⁺, comprising the following steps: 1) treating waste waterto be treated by cooling crystallization to obtain crystalline solutionthat contains sodium sulfate crystal, wherein the waste water to betreated contains the waste water containing ammonium salts; 2) treatingthe crystalline solution that contains sodium sulfate crystal by firstsolid-liquid separation, and treating the liquid phase obtained in thefirst solid-liquid separation by first evaporation, to obtain firstammonia-containing vapor and first concentrated solution that containssodium chloride crystal; 3) treating the first concentrated solutionthat contains sodium chloride crystal by second solid-liquid separation;wherein the pH of the waste water to be treated is adjusted to a valuegreater than 7, before the waste water to be treated is treated by thecooling crystallization; in the waste water to be treated, theconcentration of SO₄ ²⁻ is 0.01 mol/L or higher, and the concentrationof Cl⁻ is 5.2 mol/L or lower.
 10. The method according to claim 9,wherein the waste water to be treated is the waste water containingammonium salts; or the waste water to be treated is mixed solution ofthe waste water containing ammonium salts and at least a part of theliquid phase obtained in the second solid-liquid separation; preferably,in the waste water to be treated, the concentration of SO₄ ²⁻ is 0.1mol/L or higher, more preferably is 0.2 mol/L or higher; preferably, inthe waste water to be treated, the concentration of Cl⁻ is 4.5 mol/L orlower; preferably, in relation to 1 mol SO₄ ²⁻ contained in the liquidphase obtained in the first solid-liquid separation, the Cl⁻ containedin the liquid phase obtained in the first solid-liquid separation is7.15 mol or more; preferably, the pH of the waste water to be treated isadjusted to a value equal to or greater than 8, before the waste waterto be treated is treated by the cooling crystallization; preferably, thepH value of the liquid phase obtained in the first solid-liquidseparation is adjusted to a value greater than 9, more preferablygreater than 10.8, before the liquid phase obtained in the firstsolid-liquid separation is treated by the first evaporation; preferably,the pH value is adjusted by means of NaOH.
 11. The method according toclaim 9, wherein before the second solid-liquid separation is executed,the first concentrated solution that contains sodium chloride crystal istreated by cooling treatment to obtain treated solution that containssodium chloride crystal; then the treated solution that contains sodiumchloride crystal is treated by the second solid-liquid separation;preferably, the first concentrated solution that contains sodiumchloride crystal, which is obtained in the step 2), is firstconcentrated solution that contains sodium chloride crystal and sodiumsulfate crystal, and the sodium sulfate crystal in the firstconcentrated solution that contains sodium chloride crystal and sodiumsulfate crystal is dissolved through the cooling treatment; preferably,the conditions of the cooling treatment include: temperature: 13°C.-100° C., preferably 15° C.-45° C., more preferably 15° C.-35° C.,further preferably 17.9° C.-35° C.; preferably, the conditions of thecooling treatment include: time: 5 min. or longer, preferably 5 min.-120min., more preferably 30 min.-90 min.
 12. The method according to claim9, wherein the waste water to be treated is concentrated to obtain firstammonia-containing vapor and concentrated waste water to be treatedbefore the waste water to be treated is treated by the coolingcrystallization; preferably, the pH value of the waste water to betreated is adjusted to a value greater than 9, more preferably greaterthan 10.8, before the waste water to be treated is concentrated;preferably, the pH value is adjusted by means of NaOH.
 13. The methodaccording to claim 9, wherein the liquid phase obtained in the firstsolid-liquid separation is treated by concentrating treatment, beforethe liquid phase obtained in the first solid-liquid separation istreated by the first evaporation; preferably, the concentratingtreatment is executed in a way that no crystal precipitates from theliquid phase obtained in the first solid-liquid separation; preferably,the concentrating treatment is executed through a reverse osmosisprocess or electrodialysis process; preferably, the concentratingtreatment is executed through an electrodialysis process.
 14. The methodaccording to claim 9, wherein the conditions of the coolingcrystallization include: temperature: −21.7° C.-17.5° C., preferably−20° C.-5° C., more preferably −10° C.-5° C., further preferably −10°C.-0° C.; preferably, the conditions of the cooling crystallizationinclude: time: 5 min. or longer, preferably 60 min.-180 min., morepreferably 90 min.-150 min; preferably, wherein the conditions of thefirst evaporation include: temperature: 35° C. or above; pressure: −98kPa or above; preferably, the conditions of the first evaporationinclude: temperature: 45° C.-175° C.; pressure: −95 kPa-653 kPa;preferably, the conditions of the first evaporation include:temperature: 60° C.-175° C.; pressure: −87 kPa-653 kPa; preferably, theconditions of the first evaporation include: temperature: 75° C.-175°C.; pressure: −73 kPa-653 kPa; preferably, the conditions of the firstevaporation include: temperature: 80° C.-130° C.; pressure: −66 kPa-117kPa; preferably, the conditions of the first evaporation include:temperature: 95° C.-110° C.; pressure: −37 kPa-12 kPa.
 15. A method fortreating waste water containing ammonium salts that contains NH₄ ⁺, SO₄²⁻, Cl⁻ and Na⁺, comprising the following steps: 1) treating waste waterto be treated by second evaporation, to obtain second ammonia-containingvapor and second concentrated solution that contains sodium sulfatecrystal, wherein the waste water to be treated contains the waste watercontaining ammonium salts; 2) treating the second concentrated solutionthat contains sodium sulfate crystal by third solid-liquid separation,and treating the liquid phase obtained in the third solid-liquidseparation by cooling crystallization, to obtain crystalline solutionthat contains sodium sulfate crystal; 3) treating the crystallinesolution that contains sodium sulfate crystal by fourth solid-liquidseparation, and treating the liquid phase obtained in the fourthsolid-liquid separation by third evaporation, to obtain thirdammonia-containing vapor and third concentrated solution that containssodium chloride crystal; 4) treating the third concentrated solutionthat contains sodium chloride crystal by fifth solid-liquid separation;wherein the pH of the waste water to be treated is adjusted to a valuegreater than 9, before the waste water to be treated is treated by thesecond evaporation; in relation to 1 mol SO₄ ²⁻ contained in the wastewater to be treated, the Cl⁻ contained in the waste water to be treatedis 14 mol or less; the second evaporation is executed in a way that nosodium chloride crystallizes and precipitates.
 16. The method accordingto claim 15, wherein the waste water to be treated is the waste watercontaining ammonium salts; or the waste water to be treated is mixedsolution of the waste water containing ammonium salts and at least apart of the liquid phase obtained in the fifth solid-liquid separation;preferably, in the liquid phase obtained in the third solid-liquidseparation, the concentration of SO₄ ²⁻ is 0.01 mol/L or higher, and theconcentration of Cl⁻ is 5.2 mol/L or lower; more preferably, in theliquid phase obtained in the third solid-liquid separation, theconcentration of SO₄ ²⁻ is 0.01 mol/L or higher, and the concentrationof Cl⁻ is 5.0 mol/L or lower; preferably, in relation to 1 mol SO₄ ²⁻contained in the liquid phase obtained in the fourth solid-liquidseparation, the Cl⁻ contained in the liquid phase obtained in the fourthsolid-liquid separation is 7.15 mol or more; preferably, the pH value ofthe waste water to be treated is adjusted to a value greater than 10.8,before the waste water to be treated is treated by the secondevaporation; preferably, the pH value is adjusted by means of NaOH. 17.The method according to claim 15, wherein through the secondevaporation, the concentration of sodium chloride in the secondconcentrated solution is X or lower, wherein X is the concentration ofsodium chloride in the second concentrated solution when both sodiumchloride and sodium sulfate are saturated under the conditions of thesecond evaporation; preferably, through the second evaporation, theconcentration of sodium chloride in the second concentrated solution is0.95X-0.999X; preferably, the concentration of sodium chloride in theliquid phase obtained in the third solid-liquid separation is adjustedbefore the cooling crystallization is executed, so that theconcentration of SO₄ ²⁻ in the liquid phase obtained in the thirdsolid-liquid separation is 0.01 mol/L or higher, and the concentrationof Cl⁻ in the liquid phase is 5.2 mol/L or lower; preferably, theconcentration of sodium chloride in the liquid phase obtained in thethird solid-liquid separation is adjusted by mixing the waste watercontaining ammonium salts, washing liquid for washing sodium sulfatecrystal, and/or the liquid phase obtained in the fifth solid-liquidseparation.
 18. The method according to claim 15, wherein crystallinesolution that only contains sodium sulfate crystal is obtained in thecooling crystallization; or crystalline solution that contains sodiumsulfate crystal and sodium chloride crystal is obtained in the coolingcrystallization; preferably, the solid phase obtained in the fourthsolid-liquid separation is returned the position just before the secondevaporation.
 19. The method according to claim 15, wherein the thirdevaporation is executed in a way that no sodium sulfate crystallizes andprecipitates, preferably, through the third evaporation, theconcentration of sodium sulfate in the third concentrated solution is Yor lower, where Y is the concentration of sodium sulfate in the thirdconcentrated solution when both sodium sulfate and sodium chloride aresaturated under the conditions of the third evaporation; preferably,through the third evaporation, the concentration of sodium sulfate inthe third concentrated solution is 0.9Y-0.99Y.
 20. The method accordingto claim 15, wherein before the fifth solid-liquid separation isexecuted, the third concentrated solution that contains sodium chloridecrystal is treated by cooling treatment to obtain treated solution thatcontains sodium chloride crystal; then the treated solution thatcontains sodium chloride crystal is treated by the fifth solid-liquidseparation; preferably, the third concentrated solution that containssodium chloride crystal is third concentrated solution that containssodium chloride crystal and sodium sulfate crystal, and the sodiumsulfate crystal in the third concentrated solution that contains sodiumchloride crystal and sodium sulfate crystal is dissolved through thecooling treatment; preferably, the conditions of the third evaporationinclude: temperature: 35° C. or above; pressure: −98 kPa or above;preferably, the conditions of the third evaporation include:temperature: 45° C.-175° C.; pressure: −95 kPa-653 kPa; preferably, theconditions of the third evaporation include: temperature: 60° C.-175°C.; pressure: −87 kPa-653 kPa; preferably, the conditions of the thirdevaporation include: temperature: 75° C.-175° C.; pressure: −73 kPa-653kPa; preferably, the conditions of the third evaporation include:temperature: 80° C.-130° C.; pressure: −66 kPa-117 kPa; preferably, theconditions of the third evaporation include: temperature: 95° C.-110°C.; pressure: −37 kPa-12 kPa; preferably, the conditions of the thirdevaporation include: temperature: 105° C.-107° C.; pressure: −8 kPa-0kPa; preferably, the conditions of the cooling treatment include:temperature: 13° C.-100° C., preferably 15° C.-45° C., more preferably15° C.-35° C., further preferably 17.9° C.-35° C.; preferably, theconditions of the cooling treatment include: time: 5 min. or longer,preferably 5 min.-120 min., more preferably 45 min.-90 min.
 21. Themethod according to claim 15, wherein the conditions of the secondevaporation include: temperature: 35° C. or above; pressure: −98 kPa orabove; preferably, the conditions of the second evaporation include:temperature: 75° C.-130° C.; pressure: −73 kPa-117 kPa; preferably, theconditions of the second evaporation include: temperature: 85° C.-130°C.; pressure: −58 kPa-117 kPa; preferably, the conditions of the secondevaporation include: temperature: 95° C.-110° C.; pressure: −37 kPa-12kPa; preferably, the second evaporation is executed with a MVRevaporation device.
 22. The method according to claim 15, wherein theconditions of the cooling crystallization include: temperature: −21.7°C.-17.5° C., preferably −20° C.-5° C., more preferably −10° C.-5° C.,further preferably −10° C.-0° C.; preferably, the conditions of thecooling crystallization include: time: 5 min. or longer, preferably 60min.-180 min., more preferably 90 min.-150 min.
 23. The method accordingto claim 15, wherein the conditions of the third evaporation include:temperature: 17.5° C. or above; pressure: −101 kPa or above; preferably,the conditions of the third evaporation include: temperature: 35°C.-110° C.; pressure: −98 kPa-12 kPa; preferably, the conditions of thethird evaporation include: temperature: 45° C.-110° C.; pressure: −95kPa-12 kPa.
 24. A method for treating waste water containing ammoniumsalts that contains NH₄ ⁺, SO₄ ²⁻, Cl⁻ and Na⁺, comprising the followingsteps: 1) treating waste water to be treated by fourth evaporation, toobtain fourth ammonia-containing vapor and fourth concentrated solutionthat contains sodium chloride crystal, wherein the waste water to betreated contains the waste water containing ammonium salts; 2) treatingthe fourth concentrated solution that contains sodium chloride crystalby sixth solid-liquid separation, and treating the liquid phase obtainedin the sixth solid-liquid separation by cooling crystallization, toobtain crystalline solution that contains sodium sulfate crystal; 3)treating the concentrated solution that contains sodium sulfate crystalby seventh solid-liquid separation; wherein the pH of the waste water tobe treated is adjusted to a value equal to or greater than 9, before thewaste water to be treated is treated by the fourth evaporation; inrelation to 1 mol SO₄ ²⁻ contained in the waste water to be treated, theCl⁻ contained in the waste water to be treated is 7.15 mol or more; thecooling crystallization is executed in a way that no sodium chloridecrystallizes and precipitates.
 25. The method according to claim 24,wherein the waste water to be treated is the waste water containingammonium salts; or the waste water to be treated is mixed solution ofthe waste water containing ammonium salts and at least a part of theliquid phase obtained in the seventh solid-liquid separation;preferably, in relation to 1 mol SO₄ ²⁻ contained in the waste water tobe treated, the Cl⁻ contained in the waste water to be treated is 8 molor more, more preferably is 9.5 mol or more; preferably, the pH of thewaste water to be treated is adjusted to a value equal to or greaterthan 10.8, before the waste water to be treated is treated by the fourthevaporation; preferably, the concentration of SO₄ ²⁻ in the liquid phaseobtained in the sixth solid-liquid separation is controlled to be 0.01mol/L or higher, and the concentration of Cl⁻ in the liquid phase iscontrolled to be 5.2 mol/L or lower, before the liquid phase obtained inthe sixth solid-liquid separation is treated by cooling crystallization;preferably, the pH value is adjusted by means of NaOH.
 26. The methodaccording to claim 24, wherein before the sixth solid-liquid separationis executed, the fourth concentrated solution that contains sodiumchloride crystal is treated by cooling treatment to obtain treatedsolution that contains sodium chloride crystal; then the treatedsolution that contains sodium chloride crystal is treated by the sixthsolid-liquid separation; preferably, the fourth concentrated solutionthat contains sodium chloride crystal, which is obtained in the step 1),is fourth concentrated solution that contains sodium chloride crystaland sodium sulfate crystal, and the sodium sulfate crystal in the fourthconcentrated solution that contains sodium chloride crystal and sodiumsulfate crystal is dissolved through the cooling treatment; preferably,the conditions of the cooling treatment include: temperature: 13°C.-100° C., preferably 16° C.-45° C., more preferably 16.5° C.-35° C.,further preferably 17.9° C.-31.5° C.; preferably, the conditions of thecooling treatment include: time: 5 min. or longer, preferably 5 min.-120min., more preferably 45 min.-90 min.
 27. The method according to claim24, wherein the waste water to be treated is concentrated to obtainfourth ammonia-containing vapor and concentrated waste water to betreated before the waste water to be treated is treated by the fourthevaporation.
 28. The method according to claim 24, wherein through thefourth evaporation, the concentration of sodium sulfate in the fourthconcentrated solution is Y or lower, where Y is the concentration ofsodium sulfate in the fourth concentrated solution when both sodiumsulfate and sodium chloride are saturated under the conditions of thefourth evaporation; preferably, through the fourth evaporation, theconcentration of sodium sulfate in the fourth concentrated solution is0.9Y-0.99Y.
 29. The method according to claim 24, wherein the conditionsof the fourth evaporation include: temperature: 35° C. or above;pressure: −98 kPa or above; preferably, the conditions of the fourthevaporation include: temperature: 45° C.-175° C.; pressure: −95 kPa-653kPa; preferably, the conditions of the fourth evaporation include:temperature: 60° C.-160° C.; pressure: −87 kPa-414 kPa; preferably, theconditions of the fourth evaporation include: temperature: 75° C.-150°C.; pressure: −73 kPa-292 kPa; preferably, the conditions of the fourthevaporation include: temperature: 80° C.-130° C.; pressure: −66 kPa-117kPa; preferably, the conditions of the fourth evaporation include:temperature: 95° C.-110° C.; pressure: −37 kPa-12 kPa; preferably, theconditions of the cooling crystallization include: temperature: −21.7°C.-17.5° C., preferably −20° C.-5° C., more preferably −10° C.-5° C.,further preferably −10° C.-0° C.; preferably, the conditions of thecooling crystallization include: time: 5 min. or longer, preferably 60min.-180 min., more preferably 90 min.-150 min.